For the first time that I have heard of Sofia walked in on Nick while he was cheating. He didn't expect her and she got a whole lot more than she bargained for when she opened the door. I think he had agreed there would be no more cheating. There would be no more threesomes or hookers or going to strip clubs and there would be no more coke. She didn't catch him at cheating for awhile and they were headed to the altar but now that's a goner for now.
For most everyone else getting caught this many times would be the end but they are unlike everyone else.