I agree. We call it the golden rule. No matter wat, once u break it, it always make someone the bad guy.well guys have this unwritten rule that you dont date another guys sister or cousin or ex or ex wife its an unwriten rule but guys know and understand this so am sure girls have the same kind of code.
also irrelevant of who your friend is with you or whoever dating her ex husband would put a strain on the friendship
And like Vinu said, u have to find out y they split in the first place. If it was me, I would hope that the is honest enough to tell me the truth, even though it might have some thing to do with me.