He's with the girl and her parents as far as I know
I would damn well want to know for sure, I wouldn't trust him nor speak to him again if this is where he has been staying. He knows exactly what your reaction to staying with this girl will be.
Even if you did decide to take him back and make it a condition that he stays away from these "friends" there's nothing to say that a few months down the line you won't be back in this situation again if he decides to visit them again. It could also be a case of the green eyed monster, or in this case monsters. His "friends" could well be jealous of the life/relationship he has with you and encourage him to mess up, not that it is an excuse as he is a grown man and responsible for his actions, even if the mates are saying he is under the thumb etc.... A guy who does not have the balls to say no to his mates and shows no respect for his woman Jest on cipki!!
just take that job, change the place and try to be happy without him, the other good things will follow. don't waste your life, it is too short.
Good luck with whatever you decide.