The only way this should bother you is if you still have feelings for her and it sounds like you do. So I understand where you're coming from but at the same time, there's a reason you two aren't together anymore so chalk it up as a loss and move on. Girls will come and go, but friends are hard to come by. If your boy had gone behind your back and was messing with this chic while you two were together, that's one thing. But you guys are not together anymore so she's open game. Don't even trip man, she's the one who's gonna end up looking like a skank if she keeps going from friend to friend, feel me? Too many chics out there to be worried about this one. Have you talked with your buddy about this? I mean, maybe she invited him cause she's got a friend she wanted him to meet, you don't know what's up yet. Talk to your boy and then get back to us.