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...
close, very close. but the underlying factor was Tony thought Chrissy was bad luck,not only for Chrissy's kid but for TONY and the family. Kind of alluded to in the last episode that black cat looking at Chrissy's picture. Tony gave Chrissy probably more than 9 chances to straighten up before he killed him. There are several subplots going on. Tony not banging Skiff, Chrissy meeting her at AA and banging her, Tony meeting Chrissy's Vegas trim and doing shrooms saying all the crazy stuff he says. Classic Sopranos.
