Do the MCs have to be antagonists?

I'm not very experienced with writing romance so I'm confused about this. Some points I've read:

• their external goals should oppose each other to drive plot (then they can perhaps solve their internal issues and reach a compromise)

• another blog says that such a compromise is an unsatisfying cop out so it doesn't make sense to have external goals in conflict since ideally, only one character should achieve that goal.

• they can work together but run into some emotional conflict (ex. one is overprotective, while the other is overly independent)

I'm sure there isn't one set way to create the proper tension, but I'm wondering if I've objectively cast the wrong character as an antagonist. There are no actual bad guys in my WIP so far-- I just pictured my two heroes, who fall in love, trying to win over a third stubborn character, the most logical antagonist.

I don't think it's 3 protags (although all 3 are "good guys"), but I'm not sure if there are 2 protags and 1 antag, or 1 protag, 1 lover, 1 antag, and the roles could switch. I couldn't find info on writing threesomes and certainly no handy hero/heroine charts. Because of the nature of MC1, I don't think it can pass as a legit love triangle either, although I definitely want some jealousy involved.

Long ago, MC1 got divided into MC1a and MC1b, who lead completely different lives, each unaware that the other existed.

MC1a, a hermit, meets MC2, a normal modern guy, and they end up together as the main couple. After MC1a finds out that MC1b exists, he experiences envy and regret, and decides that reuniting them would improve him. MC1b has worked very hard for his self-determination and doesn't want to reunite, which causes him to be the sympathetic antagonist to MC1a and/or MC2.

MC2 may initially encourage MC1a's pursuit of MC1b, but become jealous when it starts to work, fearing that if MC1a reunites, he won't need to rely on MC2 any longer. This would mean MC2 could temporarily be the antagonist to MC1a. I'm not sure how to chart such a switch in function. I'm afraid if I can't put everything into some kind of logical chart, that I'll end up with a weak foundation.

I've read that each lead needs a goal, but I'm not sure if MC2 and MC1a should pursue the same external goal with different motivations (ex. convincing MC1b to reunite), then get knocked off-course into a protag/antag dynamic until all three work it out, or if MC2 needs to start with his own separate external goal before even meeting MC1a (ex. he's a wannabe historian investigating the suspicious fire that killed the person who split MC1 and the only living witness, MC1b, won't talk about it-- it's logical, but I find it pretty dry and perhaps too complicated compared to a shared goal that gets split). I'm not sure if the goal of reconciling MC1a and b, then dealing with MC2's jealousy is enough to sustain a novel either. I don't know any experienced writers to bounce or critique ideas with.