give her a kiss and run
If you still like her or want to be her friend, then yes.
Tell him that e has a girl friend and that you already broke up. If you still like him, ask him why he's flirting with you. And why he's doing so while he has a girlfriend. See what goes on then!
If you want your friend to still be your friend, hang out with him. You might find out what he likes in his girlfriend and she could be your friend too. Friends do this for each other.
The X, and here's why, it would be akward betwee you and your best friend if you and his sis' broke up
tell girlfriend the truth
understand and be her close friend and maybe let her have a brake from you and she will maybe realise how much she misses you and your commitment.
you have to be calm and see if the girl is really worth all the problem and have a word with your girlfriend ex and ask him how she broke up with him and compare your situation and his.
If you have feelings for him still, let him know
yea you should cause he might feel the same way
no you shouldn't your friend will become your enemy you should ask her is it alright trust me been there done that
If you want to be his girlfriend, tell her how u feel. If not, you should stop, 'benefiting' with him. It is not right to his girlfriend, unless she is okay with it, tho, it's not likely..
You should get over yourself and marry a pig