If he's going to be rude and mean to his friends, I think you should stop bothering for the present time. If Lorna is actually as crazy as she sounds, and Dave is generally a normal sort of person, I should think he will come to his senses soon enough. You can still invite him to stuff, but don't make complicated plans just to accommodate his girlfriend. Like, you can call him up and say that you're playing cricket at whatever time, and that he can come if he wants. Then he can choose what he wants to do. Maybe he will be silly and ignore his friends at first, but most sensible people would start to miss them after a while. Maybe he needs to stand on his own two feet and be forced to make that decision himself (if his friends and his girlfriend are fighting and everyone is vying for his time, I guess it becomes harder for him to pick what he actually wants because all his time is being taken up by trying to keep everyone happy. Plus, badgering him about it is more likely to push him away and into the arms of Crazy Lorna). Personally, I think he is being a bit of a jerk right now, and there's not much you can do about it except be ready to rekindle your friendship when he stops being so crazy. It is nice that you care though, so do not feel bad because it seems you have done as much as you can really.