In a single POV romance, the protagonist is the point-of-view character, and the antagonist is that character’s love interest. In a dual POV romance, the point-of-view characters are each other’s antagonists.
This doesn’t mean the story can’t also have one or more external antagonists who come into conflict with the point-of-view character(s) and make it harder for their love to conquer all. Your characters might even be up against a fearsome villain. But in a romance, the external plot is secondary to the love part of the story (think of a romance like the opposite of, for example, a sci-fi story with a strong romantic subplot).
Another way to think of a protagonist/antagonist relationship is two people after the same goal, and they fight each other to get it. This is true with the lovers in a romance. Both are after the same goal—love—but instead of one having to lose to the other, they will both win when they work out the issues between them. Sometimes, one character will be pushing for the love, and the other will be resisting the love (even though they also want it). In cases like this, the protagonist/antagonist relationship can clearly be seen.
In many stories, the climax will be a final battle between the protagonist and antagonist. This is also true in romance, where there will almost always be a final confrontation between the lovers before they commit fully to their relationship and live happily ever after.
Each Romance Writing Simplified post features a few hundred words on one aspect of romance writing. The goal is to present these complex ideas in the simplest terms possible.