The way I see it, Chris was a ticking time bomb from the start and the ZA was the final thing to set him off along with losing his mother. However that does not give him any excuse or reason to behave the way he is now. Shit happens that's a part of life, but he chose to deal with it by acting like a pretentious little shit. He wanted to kill someone and so when he got that opportunity thanks to the surviving victim from that plane crash, he was thirsty for more. Because if you look back on that scene Chris is killing the guy slow and watching him as he does because he's trying to savor that moment.

Then he gets another chance with that dime store looking leo dicrapio pirate they take prisoner. Only Chris fails at killing him and thus becomes a walker.
Chris wanted to see Madison die, and he was probably thinking about what would happen if he killed both her and Alicia that night. Then he runs away and Travis goes after him, and then Chris takes a little kid hostage. At this point Chris gives no ****s about humanity because his is gone. And we see it after he kills that farmer and feels nothing and then tries to help the bros kill an injured James because they view him as weak. By that point Chris is too far gone and that's why Travis can't reach him, but I think deep down Travis knows this but still lives in denial.

And now based on spoilers we're going to learn that

Good riddance btw.