Two things. First, make sure the argument escalates. It can't just be "you did it," "I did not do it," repeated ad infinitum. It has to get worse and worse until someone goes too far, and the scene ends. Sort of: he hints that she did it, and she laughs it off, and he says he really means it, and she tries reasoning, and he's unreasonable, and so on. Or they're arguing about the spaghetti that spilled on the floor (just an example), only it isn't really about the spaghetti; it's about his suspicion of her, and the crisis of the argument is when, meaning to shout "You killed the spaghetti," instead he shouts "You killed my wife."
Second. Just for the record, the h/h aren't always the protagonist and antagonist in a romance. There are situations where they both have problems that would keep them from committing to each other, and those problems are resolved in the course of struggling with another antagonist, rather than with each other.
The type of romance where the h/h are each other's antagonist is really difficult to end gracefully. If the conflict is a big misunderstanding (he thinks she killed his wife, but she didn't), then the resolution is anticlimactic, b/c the reader will think, "Well, duh, if they'd just sat down and talked it out, he'd have known the truth on page one, and who in her right mind wants to live with a man who once thought she could have committed murder? What will he think the next time someone he cares about dies in suspicious circumstances?" If the conflict is something other than a big misunderstanding (the classic land battle -- he wants the land to build his dream home on the lake, and she wants the land to turn it into high-rise apartments), then one of the h/h will win in the end, and one will be a loser, and it's kinda' hard to build a credible, lasting relationship on a win/lose situation. Sacrifice is all well and good, but about the only way that serves as a happy ending is if it turns out that one of them didn't really want what he/she thought she wanted, and then it's a little disappointing for the reader, b/c the implicit promise in the beginning is that those goals really, really matter to the characters.
Anyway, just something to think about. Not all romances have the h/h as protagonist and antagonist. Which isn't the question, but might help with the conflict, since perhaps they're conflicting with a third party, and less with each other, but they grow individually and together in the course of the conflict with the third party.
JD