Okay, with the “mad doctor” dividing a character into two characters, it sure sounds like we have some kind of sci-fi or fantasy story here (another iteration of Jekyll & Hyde?)! But whatever genre you set it in, I still need some basic, clarifying answers:
So, are your MC and Antagonist both male? And is the Protagonist/IC male or female? (You mention “a love triangle,” but that doesn’t necessarily narrow the options down much!) So, are there any females among these three characters?
And what will happen in the rest of the world if the two halves of this divided character don’t reconcile?
A few disappointed friends? A messed-up social circle? Confusion about which half to invite over for a holiday party?
Or something more impactful, like the Protagonist-reconciler losing his/her “only chance at love”? Or having his/her life threatened by either an out-of-control MC or Antagonist, or both?
Or the MC’s company/empire/venture failing and people losing their jobs and security? Or a town/nation/world at war, because this character divided against itself has so much self-hatred that it cannot tolerate the idea of reconciliation?
Basically, in whatever world where they exist, these three characters should have at least some connection to a larger world where reconciling (or failing to reconcile) this two-halved character into one will make some dramatic difference that an audience can see.
And don’t worry about constructing a “perfect” Overall Story at this point! Answer some of my questions above, and your ideas on the OS should begin to blossom toward a useable version…