Paul gave him the money to pay back Jane, after the catfishing incident (otherwise Jane wouldn't have seen any of her money again). So he has still been hanging around to pay back Paul - & Paul doesn't realise he is getting the money by breaking into people's houses etc!. He needed a place to stay (couldn't obviously stay at the backpackers), so I think it was just a coincidence that he answered Mackenzie's advert for a housemate (I hope I have remembered all that correctly!).