What should have I done in this type of situation?

Gotta love Facebook. It sounds like you know what you should have done, not that there is a definate right or wrong way. In my opinion, I think you two could be friends, but I can see the boyfriend being jealous. Try putting yourself in his position, your gf talking to another guy (maybe more than she does you) how would you feel; I think maybe a little threatened. In a case like that you could always try and explain but, most likely, that will not help. I think the best way would have just to let it go and just say okay. If the girl really wanted to stay friends she would explain to her boyfriend (that you two are only friends) and then explain to you (that it wasn't her on facebook and she wants to stay friends). I would have stayed out of it and let the girl do the work, it would cause less drama and would probably end better. Knowing that most guys (sorry for the stereotyping) like to defend their pride and what not, you and her boyfriend would want to fight to see who is better (or whatever other reason guys fight). So I think you handled the situation okay but there might have been a better way. :) Hope that helped!