My Cousin Rachel - du Maurier

I am a terrible skimmer. I read the book up to the point where Rachel arrived, far enough to see that the implication was that she was going to charm Philip and poison him as well.

Flipped to the back few pages and saw about the bridge being constructed. She had an accident and died and Philip had set it up. It was not clear because i have not had the patience to read it properly whether she had been poisoning the pair of them or not.

So what did happen? Was he morose at the end with guilt for engineering her death or because he realised she had not actually poisoned anyone?