>>94678193>Eclipsa is a major threat that would require his full attention if he wants to actually help Star deal with her.
Not yet, though. I do agree that she'll be a main antagonist at some point, but it won't be so immediate it'd require Marco to just remain in Mewni - hell, the big showdown will probably happen sometime in season 4. So Marco will most likely return to Earth in the meanwhile and will just pop between Earth and Mewni.
And why wouldn't it be fair to Jackie? Marco's been spending a lot of time with Star - hell, she was living at his house - already when they were just starting to get together. Why would she now be super angry that Marco wants to continue hanging with Star, his best friend?>If she confronts him about how neglectful he's been
How neglectful has he been, exactly? She seemed quite happy about their friendship all the way until Star's confession (which they probably do need to talk about), then Marco was really down for x time, maybe some days, before going for a quick visit to see Star - and had to stay for some days because it was a literal life and death situation. At the most, he's been neglectful because he didn't know what was going on with his best friend and then it turned out that bestie's life, her family's life and her entire country was in terrible danger. Of course he had to help out. Jackie will most likely understand that, and possibly admire Marco for being a stand up guy, brave, reliable, persistent and kinda heroic.
People seem to want to imagine that Jackie would, for whatever reason, be super upset and throw a tantrum and either break up in a rage or wistfully tell Marco to go to Star. But I don't think that'll happen - Marco's spent so long pining after Jackie that if there's any issues, most likely he'd just try to spend more time with her and be a better bf, instead of going lol whatever bish I'm dropping this relationship