Would you consider this a socipath?

He doesn't sound like a sociopath, just a horrible person. He's acting very childishly trying to manipulate your friend. I don't think you're overreacting because obviously you're going to want to protect your friend and want the best for her. The best thing you can do is stick by your friend and let her work it out for herself. If she asks your opinion on things he says/does etc. then give it but without being malicious. Remind your friend that she is a great person and does not have to put up with this sort of behaviour. Lot's of girls have poor self confidence and are easy prey for guys like this (I was one), but it doesn't help when your friends are constantly putting you under pressure to break up. I found that friends who supported me throughout the relationship and avoided criticizing my ex (unless they were asked their opinion) were the ones who were there for me when we broke up, and are still my friends now. Hope the situation works out.