20-month-old boy, seeking some advice

My wife and I (but mostly she) have been training out son to use the potty for what seems like ages at this point. I believe we began in earnest about six months ago, when he was about 14 months old. It has been a difficult and prolonged journey, but we have made significant headway. Our son has not really worn a diaper except overnight for the last 1-2 months, and he always tells us when he has to poop. But - peeing is another issue entirely!

He refuses to go to the potty when he has to pee. He doesn't even tell us, like when he has to poop. We usually have to notice that he has begun to wet his pants, and then convince him, beg him, to come to the potty. He willfully resists the bathroom at this point - telling us No and refusing to come to the bathroom. He often wets himself or messes on the floor because of his resistance. We are really at a loss to understand why he resists peeing on the potty so much.

My intuition tells me that we just have to wait - that this is a part of the learning process, and the fact that we have made so much progress before 2 years old is a significant feat on its own. He is not afraid of the bathroom or anything like that - I just think he gets caught up in what he's doing, and doesn't want to stop playing, etc. But for my wife's sake, I come seeking help and advice on what to do. She is at her wit's end, and feels like she has ruined everything (and there's no convincing her otherwise).

I'm happy to provide more details if that would help. It seems like we've tried everything, but despite all of our progress, he are stuck, and have been for a while, with the pee.