Based off of this post
So, Tiberius and Tony are dating. However, Tiberius starts feeling like Tony isn’t enough, and being the mega-douche that he is, he gives Tony an ultimatum, either we have an open relationship or we’re done.
Tony, poor baby Tony, terrified of losing the one “friend”, the one constant thing he’s had for 18 years, reluctantly agrees.
Fast forward 1 month. Tiberius, the mega-douche, high and dry, watching as Tony is wooed by a smitten and awed Steve Rogers. Steve, though unhappy with the “open” relationship, not being able to resist spending any time Tony would give him. Tony, for the first time in his life, being wanted and adored without any conditions or ultimatums. Tiberius spying on Tony’s dates, wondering what that two-bit mongrel, with barely 5 dollars to rub together, could be saying, that was making Tony laugh quite that hard.
Steve introducing Tony to his friends, silencing Bucky with a single look, keeping them from mentioning anything about Tiberius and the complicated relationship.
Natasha sharpening her knives, and Clint flanking Tony whenever Tiberius comes around to pick him up. Bruce shyly talking shop with Tony Stark, Thor enthusiastically welcoming Tony into the friend group and introducing him to Jane.
Tiberius enviously looking on as Tony steadily gains a support system, and actual friends who don’t care about Anthony Edward Stark, only Tony, the Mechanic.
Tiberius, refusing to kiss Tony, cruelly mentioning peasant disease, STDs, dammit Tony, why are you around them so much! they will never understand you.
Head ducked, eyes closed, Tony, for the first time in his life, removing himself from the equation. Tony looking up, eyes ablaze, pissed off. How dare anyone talk about his friends that way?
Tiberius giving Tony another ultimatum, them or me, Tony. You can’t have both. This was a mistake. There is no one else for the two of us.
Tony’s eyes catching on the paint on his hands, the same hands Steve had physically directed, Steve’s body pressed behind him, his head on Tony’s shoulder, into creating a painting for a gallery show.
Tony smiling, and saying “It’s them, Ty. It’s always him. Goodbye, Ty.”
Tony walking out of his apartment, running towards Steve’s. Tony jumping into Steve’s bed, and showering him with kisses, unabashed and free for the first time since this whole mess started.
Steve waking up to a manic Tony, with wind-swept hair and tender hands.
Steve and Tony making love for the first time, as Tiberius collects his stuff from Tony’s apartment.