I have two friends who I am talking with over the Skype. We get along just fine, there's just one tiny problem with one of them. Everytime my second friend mentions even the name of his girlfriend, the first one suddenly gets upset and annoyed about that. I've tried talking to him about it, but he says it's something he can't control, it's his "trigger" and he doesn't know why he acts that way. He rarely spoke to her, even admitted that she's a decent person, but he still gets upset over mentioning her. He also says it's not jealousy. He suffers from neurosis, but I don't know if that's why. He even spoke about it with the other friend, but the latter got mad at him and said he's overreacting and that he's not going to pretend he doesn't have a girlfriend. I don't know what to do anymore, I'm afraid they will both end up jumping to each others throats some day.