I headcannon that Starscream (and probably other Decepticons) are touch starved, and deserves to be treated nicely for once. You mentioned in another post that Starscream missed his trine, and I agree whole heartedly. Now, if Starscream did join the Autobots and got to a healthier environment, how’d you think he’d adjust? Who would he open up to about his trine? (Sorry, this was long)
Hmmm, an interesting question. One which I will gladly expand on and answer to the best of my ability. (Oh and don't worry about your request being long, I don't mind!)
A Long Awaited Defection
After having finally had it with Megatron's consistent failures as a leader and his dark energon induced madness, Starscream would finally take the leap of faith he had been teetering on the edge of making for some time. After removing his Decepticon badge, Starscream would take a few precious belongings and some Decepticon data before fleeing the nemesis. He would then contact the Autobots using his stolen data as incentive.
It would be a tense discussion to say the least, that with Starscream's many crimes and whatnot. However Optimus has always been the forgiving sort and knows the darkness that lives within Megatron. He would, after some questioning, accept Starscream into their ranks under the condition that he be supervised and have his wings bound for a trail period. The rest of the team, especially Arcee, would not be fond of this choice, but Optimus knows a hurt mech when he sees one, and he would be unwilling to leave Starscream to suffer under Megatron.
Starscream would be brought back to base and have his wings bound before being handed off to the bot least likely to murder him in recharge. For his own safety, Starscream's assigned partner would be Bumblebee as the scout tends to more often than not match his Sire in mentality. Starscream would share quarters with Bumblebee and do basically everything with the scout except go on missions. On the days where Bumblebee is sent out on a mission, Starscream's guardianship would fall to either Optimus, or if he is not available, Ratchet.
Given enough time, some interesting relationships would form.
Starscream's Integration
It is not easy for Starscream to get settled with the Autobots. He has spent far too long in Decepticon society where power is key and any and all weaknesses are exploited ruthlessly. Despite the decision to join them being his choice, Starscream is downright awful to be around for the first few weeks as he figures out how the Autobots work. Bumblebee would try to be kind when possible but end up treating Starscream like a stray cat for the most part. He may not be his Sire, but he most certainly inherited the ability to sense small unattended things with a pulse that need love and protection.
Eventually Starscream would begin to leave his space and engage with others around base. It would be small at first, the seeker only ever muttering a suggestion or snarky comment before scurrying away in fear of punishment. But as he grows more comfortable, his coding would come to life again after millennia of being dormant and demand he search for family and companionship. This would lead him to express himself more and begin the natural process of integrating into what his coding recognizes as his new flock.
In light of this, despite his best efforts to be friendly in his own prideful way, his relationship with Arcee and Bulkhead would be turbulent at the best of times, even in the far future. However they have an unspoken agreement of sorts. They protect each other and work together when required, perhaps even socializing when a mutual friend is present, but other than that they have no ties. This is perfectly acceptable to both parties as neither have any desire to associate with the other.
Wheeljack would be pretty chill with Starscream's presence, although it would take a while for Starscream to warm up to the wrecker. After a while they would even develop a friendship around their shared love of science. Starscream supplying Wheeljack with the more intricate knowledge needed to create more complex things and Wheeljack doing most of the heavy lifting. Perhaps their friendship is not the most emotionally bonding, but Starscream and Wheeljack have a friendship unique to them. They are not close enough in Starscream's mind to be kin, but they have enough compatibility between them to have Starscream consider the wreaker a wing-mate, that is if the grounder could fly.
Ultra Magnus would be highly distrustful of Starscream and the seeker would steer clear of him for a long time due to how the commanders gaze reminds him of Megatron. However after Starscream is fully accepted into the Autobots and proves his worth in battle and assisting Ratchet in his scientific endeavors, Ultra Magnus's opinion of him would grow. Eventually they would bond over battle tactics and strategy, together spending long nights working out plans and dealing with as much work as they can before their workaholic Prime takes over. They would also find themselves bonding over the shared experience of trying to keep the team in order and help steer Optimus away from self sacrifice when not necessary. Their regular ritual is to drink a cube of stimulant laced energon together each morning and checking in on the other before going about their business. While also not a very emotionally invested relationship, their shared purpose binds them together in a form of brotherhood, as such Ultra Magnus is also a wing-mate in Starscream's mind.
Smokescreen would be one of the hardest for Starscream to warm up to, and vice versa. The young elite guardsman would struggle greatly trying to get used to having one of Megatron's old lieutenants hanging around. But after saving each other in a few fights and finding that they work well together, Smokescreen would begin to look up the the seeker. In return Starscream would begin to view Smokescreen as a fledgling under his supervision and take up the role of a mentor, albeit a seemingly very disinterested one. Not that he will ever admit it, but he is very proud of his grounder apprentice. The rookie does well in adapting Starscream's teachings and making them apply to his own fighting style. Not only that, but Smokescreen genuinely is interested in the stories that Starscream has to tell of Vos and flight frame culture as a whole. While there is a very low chance Starscream will ever tell his apprentice, he is very fond of him and would fight just as fiercely as Optimus to protect the youngling should the need arise.
As for Starscream and Bumblebee, their relationship started off a little rocky. Bumblebee was not fond of having to partner with Starscream and the feeling was mutual. However being the sparkling of Optimus and therefore having inherited many of his Sire's traits, Bumblebee was persistent in trying to build up a friendship with the seeker after the initial awkwardness passed. And despite Bumblebee's youth in comparison to Starscream, it did not end up taking long for them to bond. Bumblebee took the time to introduce Starscream to the Autobot lifestyle and their way of life, even going so far as to calm him whenever he woke from recharge in terror. While it did take a bit for Starscream to swallow the pride he had built to protect himself while with the Decepticons, he did eventually accept Bumblebee's kindness and even return it with some of his own.
After having lived with the Autobots for some time and having fully integrated into their team, Starscream is possessive and will gladly protect his yellow wing-mate at all costs. He regularly brings Bumblebee little things and checks up on him to make sure he is alright. He has taken up a role as a secondary caretaker for the scout when Optimus is unavailable while also simultaneously being a brotherly character. He will go above and beyond to take care of Bumblebee but will always try to remain aloof and appear uncaring. Of course Bumblebee has learned to see past this, but he kindly says nothing about it and accepts the affection when he receives it. The fact that Starscream is willing to lounge around with his wings spread while around him is proof of the seeker's trust.
Then there is Ratchet. Their relationship was strictly professional at first, but after the medic found Starscream having a bad panic attack in a storage closet things changed between them. For a time Starscream refused any and all attempts the medic made to help him deal with his mental issues. But eventually after a particularly bad nightmare Starscream broke down and spilled everything to Ratchet. Everything from his grief at the loss of his trine to the anger he feels towards the Decepticons was laid bare. And surprisingly, Ratchet understood and put aside past grievances to comfort the seeker. Since then they have been close, their relationship not needing words or being particularly public. Instead Starscream comes to Ratchet whenever he is having a bad day and they will drink some energon and do some chores around base. Sometimes they discuss Starscream's problems and other times they banter back and forth. For whatever reason Starscream feels incredibly safe around the Autobot medic and has come to see him as a protector, someone akin to a guardian. Ratchet is kind enough to not comment when Starscream cuddles up beside him or follows him around like a lost sparkling, he knows the seeker needs it.
And lastly there is Optimus, the bot who Starscream had the easiest and also the most difficult time adjusting to. The Prime's size was rather intimidating for the first few weeks, as was the knowledge that the Prime had torn mechs apart in battle before. However over time and after coming to see the kind spark and soft voice behind the stoic mask Optimus usually wears, Starscream attached himself to the Prime quickly. It was just his coding at first, it urged him to seek guidance and protection from the leader of the flock. But eventually he began seeking out the Prime for others reasons, in the beginning mainly just to feel the calming waves his field emitted. And later he sought out Optimus for true companionship, finding that they had a great deal in common and got along well bonding over dealing with the younglings and the horrors of war. Starscream couldn't explain it if he wanted to, the Prime just had an indescribable draw, one which had little difficulty pulling Starscream in. And before the seeker realized it he found himself listening to the Prime's stories and bringing him energon when he worked late at night.
Being the possessive creature that he is, Starscream lurks in the rafters and other high places to observe Optimus and to keep an optic out for potential danger toward him. No one touches his kin, especially not his flock leader and Prime. There have been several occasions where Starscream has leapt from the rafters to tackle a bot who looked a little too suspicious, even screeching at them and flaring his plating to ward them off before coming to his senses. He also hovers around Optimus and assists in his work as a cover for what he truly is doing which is taking the opportunity to be clingy. Often he hangs off Optimus's back and leans up against him when they are together as he just wants to feel the protective presence of another. In return Optimus will sometimes massage Starscream's wings, working out dents and easing tight cabling for him. It is something the former Decepticon greatly appreciates and never intends to alert Optimus to the cultural significance of. Only close kin care for each other in the way the Prime cares for him, and Starscream happily allows himself to relish in the affection from his unofficial family and flock.
Extra
Being in a healthy environment made Starscream healthier as well. His armor is bulkier and is more colorful, he is less aggressive, prideful, and arrogant. He is overall a happier bot and far more willing to express himself and speak his mind without fear.
Megatron threw a tantrum the moment he caught sight of Starscream gracefully flying through the air brandishing his bright new Autobot insignia while bombing Decepticon forces. The warlord nearly burst a wire upon receiving a well earned middle finger and a shot to the chassis from his old air commander.
Seeing their old commander so happy and doing so well on the opposing side, several Vehicon squads would also abandon ship in favor of trying their luck at becoming Autobots as well. If successful then the Autobots would then be forced to get a larger base...
