Tony had reason to believe Chris was going to rat from the very first episode, when Chris talked about his screenplay. Tony had a delusional outlook on Chris, that Chris was going to run the family as an intermediary between Tony and the captains, then become boss himself when Tony was gone. He saw Chris as the gangster son that AJ could never be. When Chris told Tony that he had gotten high that night, and Tony saw the tree branch had impaled the car seat that the baby would have been in, he came to his senses (in a sociopathic way) and came to terms that Chris really was no good, and that the company had to finally part ways with him...