In this kind of situation, all you can really do is be there as a friend for him, if it makes things worse him coming to you when with her, then that'll only make a volatile situaton worse, just don't stop caring and don't give up on him, sounds like he just needs all the friends he can get right now, its really admirable what you have done with him, but on the other hand its part and parcel of being a friend.
Maybe try and meet up with him sometime, talk to him in person about him maybe going to see someone to get some help? Its obvious that, even though you feel out of your depth with this, you're doing all you can to help and be there for the guy,
thats really all you can do for now, he needs to talk to someone who is trained to help and aid people in his situation.
Kudos to you for being there for the guy mate.