Everyone who says "Star should just accept Jarco and move on" needs to fuck off.
Look, don't get me wrong, Jarco is nice and I have nothing against Jackie. She is beautiful, she is cool. I know. We all wish we had a girl like her, and so we want Marco to score with her. It's great (even if highly unrealistic) that she likes Marco despite all his spaghetti. I'd like her to be happy in the end.
But come fucking on, they don't have what Star and Marco have. And never will. Star and Marco have some of the most amazing chemistry in animation, and their relationship has been developing since day one. Sure, they are MCs, so turning that friendly relationship into a romantic one would be a cliche - but that doesn't automatically make it bad or wrong. It wouldn't be an asspull, it comes naturally from how the show is progressing. All those tochy-feely moments, all this teasing (seriously, the fucking "Moon of Lovers"?) It would be narratively unsatisfying to leave them as friends.
Jackie and Marco clearly enjoy each other's company, there is no denying that. But that's only been for, like, the last 1.5 episodes. They barely spoke much prior, and he still hardly knows her. It still can (and will) develop into something stronger in the future episodes. But will it really last? Happening in the very middle of the show of all things. You really think it's going to stay until the end? With more SoL episodes to focus on it ontop of all the deepest lore? How and in what direction would it be developing?
It's great that Marco is succeeding with Jackie, and she is getting more focus. They will both be better characters because of it in the end. But we all know how the show is really going to end.