My boyrfriend is friends with this ex friend. She ...

I think its very rare for exes to just be friends but just listen to ur gut as long as hes not hiding anything or running in the other room to talk on phone to her u should be ok.  My boyfriend is friends with one of his exes but he will only hangout with her if i can go too.

Why does he want to hang out with someone he was only previously associated with because they were doin it? She disrespected him by cheating on him, why does he want to be her friend, why does he need to be her friend?

I can relate to what the previous answer said, it would be fun to hang out with my current girl and my ex girl......me and my ex would later laugh about what a turn on it was having my current girl friend in the room and her being totally clueless to what was really going on, it spiced things up that's for sure.

What is he talking abt i meant if its really harmless he will ask u 2 go i ddnt mean it should be a turn on omg lol.

If he has to invite you along to MAKE you believe that it is harmless then that is what us guys will do, and most girls will fall for it. They would say to themselves there is nothing between them, I KNOW that for a fact because we all hang out together..........Don't fool yourself!

Tell him how you feel, if it bothers you , he needs to stop, it is his ex. Sometimes it may not be over, dont let your self sit and worry, and get hurt over it.  You didnt say if you knew or liked her. I wouldnt like my boyfriend or husband hanging out with another woman, that had a close relationship with. It works out sometimes, but most the time not.... Good luck