My detailed timeline and take on the events of Marceline and PB’s relationship, guessing a little on specifics (some based on Obsidian so, spoilies)
1) The earliest interaction between them is at the end of Obsidian at Marceline’s concert. There’s speculation that this is when they first met, which is possible, but I think they knew each other at this point, at least a little. Maybe they’d just met and started hanging out and Marcy brought her to a concert. This is when Marceline gives PB the t-shirt. They both look younger here than the rest of the series/Obsidian.
2) In flashbacks during Obsidian, we see them hanging out in Bubblegum’s lab, definitely a little older than the shirt/concert scene. I loved these scenes because they act really immature together, like they’re just teenagers hanging out and having fun and not taking anything too seriously. It was interesting to see their dynamic here compared to their current relationship being that it just basically just feels a lot younger.
3) We see their breakup in Obsidian when Marceline sings “Woke Up” about not caring about PB and Peebs says that they’re done. What I think happened is that PB started to talk to Marceline less and less as she focused on her kingdom more (in “Varmints,” Marcy asks Bubblegum if that was why she stopped talking to her). PB didn’t ask Marceline to come to the glass kindgom, Marcy just tagged along which I think was Marcy trying to spend time with her while Bubblegum was pushing her away. In a flashback of Marceline in the bomb shelter, we see her kind of convincing herself that when people run away from her it’s because she scares them away on purpose. I think that’s partly why she sings the angry song about Bubblegum that subdues the dragon- it became really clear to her that PB doesn’t want to hang out anymore, so it’s essentially her breaking up with PB before PB breaks up with her.
4) This is when the events of the original series unfold. (Also, somewhere between flashbacks in Obsidian and these episodes, Marceline dates Ash). In Marcy and PB’s first two episodes together (“Go With Me” and “What Was Missing”), they have a similar energy to the breakup flashback in Obsidian- at each other’s throats and general dislike towards each other. Marceline’s song “I’m Just Your Problem” seems to fit with their past pretty well. During their breakup in Obsidian, PB treats Marcy like she’s unrefined and a nuisance, calling her “monster trash.” Marcy still doesn’t really know or understand why PB is angry with her when, from her point of view, PB’s the one who ended their relationship by pushing her away and acting like she didn’t want Marcy around (“I forgot what landed me on your blacklist” - “I’m Just Your Problem”).
The tension starts to melt a little when Marcy sees that PB kept the shirt she gave her, showing that PB actually always did and still does care about her.
5) “Sky Witch” is the first episode we really see them have more mature and positive interactions. Marcy asks PB to hang out which seems to imply that somewhere between “What Was Missing” and here, they slowly started to hang out again and are acting like friends. It’s unclear when in the series their rekindling turns into a relationship again but I don’t think it’s happened here yet. Time is unclear, but it’s probably been a few hundred years since they dated, so I think they’re just getting to know each other again and rebuilding trust. Their energy is similar in “Red Starved” and “Princess Day” as well. They definitely act like friends and I think there’s flirting for sure, but there seems to be a slight amount of tension in these three episodes which I think comes from their not yet addressing their breakup and talking about what happened.
6) “Varmints” and the Stakes miniseries is around when I think they start dating again. They reconcile in “Varmints” with Marceline finally asking why PB stopped talking to her, and PB admitting that she pushed Marceline away in order to focus on the Candy Kingdom. This is really big for Marceline since she never knew why Bonnie left her hanging and probably blamed herself. Since Marcy spent all this time thinking her mom abandoned her because she was afraid of her (and remembering her dad was never around and that Simon left her), Bubblegum’s tossing her aside was probably really hard for Marcy. PB’s apology and accepting that a big part of their breakup was her fault is what I think allowed them to start a relationship again.
The Stakes miniseries confirms for both of them that they really care about each other. I think this is when they get back together, probably right after its conclusion. There’s flirting throughout (“you think I’m nice?”), and we see a lot of affection, especially from PB.
7) “Broke His Crown” is the confirmation for me that they’re in a relationship again. They go on a dinner date to see Simon. It’s clear that it’s really important to Marceline for PB to have a relationship with him. This feels very much like a “meeting the parents” kind of episode. They’re more comfortable with each other, talking about hanging out in the future and generally just acting like a couple.
Two more cute episodes that point to their being in a relationship are “Ketchup” and “Marcy and Hunson.” In “Ketchup,” Marcy describes her trying to save PB while playing their personalities together in a complementary and sweet way (punk rocker Marcy and bookworm PB). In “Marcy and Hunson,” Marceline sings “Slow Dance With You” which is a really cute nod to the end of Obsidian when they dance together.
8) The series finale is where we get definitive confirmation of their relationship when they kiss. Their tense conversation beforehand about starting a war is interesting in hind sight. It’s possible that Marcy is not just scared about the war, but a little worried that PB is getting too wrapped up in her work again. Later when PB almost dies, she reassures Marcy that she’s not going anywhere. This, along with the kiss, seems to solidify the commitment they have to each other and show the seriousness of their relationship. You can really see how much both of them and their relationship have matured compared to all the flashbacks we see in Obsidian.
9) Eventually, sometime after the events of the finale, PB and Marceline move in together into Marcy’s house, go through the events of Obsidian (which is probably at least 10yrs after the finale), and are together for the rest of their lives as far as I’m concerned. :)
