It all depends on the ex I guess plus the age.
You don't need to be a man to be a gentleman. Overhere we have an expression: The real gentlemen are mostly female.

I don't think our friend goes driven by gentlemenship but to me it feels curiousity and knowing with whom the one he still feels for gets married with is the reason. This can turn into a painful experience and fights at the home front. Women aren't blind, they are not less jealous like some men state and recognize if their man loves someone else long before he knows or admits. They might turn a blind eye but know.

So I wonder how the bride feels if all ex girls show up. Perhaps all girls party together while exchanging their eperiences? Now I think about it that could be fun. 🤣