Whilst I think that Bennett's death obviously had an effect on him, I've always put his mental downward spiral down to the guilt he had to carry around. I think he blamed himself for Bennett's death, given that we weren't really told why Claire killed her, so for him it was probably because he felt that it was due to the way he 'made' her.Just so I have things clear in my head did Topher just go crazy from all that went on, like we kinda got the start if it when Bennett died, and it just progressed from there?
But more so than that, he essentially blamed himself for the way in which the world ended up. He made that technology so as far as he can see it was all his fault.
That's my interpretation anyway