Why She Pees?

My wife has a black boyfriend who we met on vacation a couple of years ago. Beginning with our first encounter and since then, he pounds her so hard that she loses control and pisses during sex. She cums vaginally too with him, more than she does with me, but the pissing is something that never happened until they started fucking.

Recently he has begun telling her to wet herself before sex, then most of the time she still continues to pee during sex. He literally told her the other day to pee in her tight jeans before stripping when she was ready to go. Without questioning him, she did, which tells me they have done this before (I'm not there for every session).

Her peeing herself wasn't really a thing for me, but the fact that she can't control herself during sex with him, plus the new thing of him getting her to wet herself while still dressed, gets me seriously horny.