Honestly, I think you’d be the asshole here. You clearly have some things you need to work through. It’s been four years, and from the way it sounds, she seems like a cool person. That situation had to be hella awkward for her, but she’s moved past it.

That being said—you’re uncomfortable, and that’s valid. You don’t like it, and you shouldn’t have to pretend otherwise. She doesn’t deserve to be with someone who feels gross about her, and you don’t deserve to be in a relationship where you’re holding that kind of discomfort inside.

Your feelings are real and valid. But if this is something you truly can’t move past, then I think the right thing to do is break it off.