I cant take it anymore

My daughter's father is ALWAYS accusing me of cheating. He's questioned me for 4 years that we have been together. Some of his theories are crazy. He has a very bad past with relationships, so I have always tried to be sympathetic.

Well, he started to accuse me of messing around with my brother in law because I liked a few of his things on facebook. Omg. I would NEVER!! It gets dropped.

My fiance watches porn a LOT. I asked to use his phone to google something and his search history is full of things like "sexy girl cheating with brother" "girl cheating on husband on phone" all different pornos...

I'm really concerned. I'm tired of being questioned. I think the porn thing is crazy and it's almost like he has this OBSESSION with me cheating. He sneaks looks at my dirty underwear, comments if I smell different or wear makeup to work, and if I have any bruises or anything like that- he thinks something is going on.

I've never cheated on him and I just cant live like this anymore. I cant keep trying to fix him... what should I do?