Is there a reason I can’t do that? Am I correct that I can change which player the antagonist is later on in the story?
Protagonist and antagonist are tricky terms because in pop story culture they’ve a lot of baggage. In Dramatica, they’re used simply to describe how characters function, not how the audience should feel about them.
So yes, an antagonist can be a romantic interest.
@LunarDynasty is right - Dramatica is more precise when it comes to these terms.
When Authors think of a romantic interest as an Antagonist what they’re really looking at is an Influence Character - who functions as an “antagonist” to the Main Character’s personal growth.