Here's a moral question for you kids.

[Protoclown]

Precisely. If you don't want something to come back and haunt you someday or don't want to end up regretting something you've done, then DON'T DO whatever it is you were debating doing.

Now, it would certainly be the gentlemanly thing for Friend A to delete the pictures, but I'm assuming that he obtained them in a fully kosher manner. In which case, they're his to hang onto if he pleases, even though Friend B's fiance may regret it and not be altogether happy about it.