Is it really worth getting all hyped up over? Be grown up about it. Obviously he's not your friend, and not at all trustworthy, so why waste another piece of your time on him?
On a separate note though, your girlfriend should be doing a little more to keep you calm. First thing she should be doing is calling him either in front of you, or texting him back in front of you to let the guy know that she's NOT interested in seeing him ever again because it's obvious what kind of person he is and does not have respect for others, if she truly feels that way.
Bottom line though is that the guy didn't say anything to you, he confronted your girlfriend. Therefore, it's her place to tell him that 'no, she's not interested in seeing him, will not be breaking up with you for him, and now that she sees how he is, has no interest in having any kind of a relationship with him.' Same thing if a girl-friend of yours and hers hit on you in the same manner. It's really YOUR place to let her know what's going on, but at the same time informing your girlfriend of it so that you can't be accused of keeping anything from her.
Just what I would do in the situation...