One thing is for sure, and thats that things cant stay the way they are now. Yourr girlfriend is afraid for Gods sake. Neither of you should live that way. I would say try and be nice about it first (just so you can say you tried if this plan doesnt work). Sit him down and tell him that the way things are now just isnt the way things are going to be from now on. He needs to start pulling his weight. You aren't his mom and shouldnt have to pick up after him (not that anyone's mom should have to do that shit anyway). If he doesnt shape up than blow up at him and threaten to kick him out. If things dont change then than just kick him out. It's your house so that means your rules. Good luck man.