This is discouraging!

So I know that girls on here post nice thing about their SIgnificant others but the post about their man cheating is just getting to me! I'm getting married in May. And my fiancé and I have had a good relationship I've always trusted him but up until recently I have felt so pranoid  just reading all these post! I feel like he is always lying to me or talking to other girls trying to get with them or he is always watching porn or he is just cheating I don't know! He has given me absolutely no proof or reason to feel this way. I think it's just all in my head but I don't know how to get past it?! I can't shake it... Any advise?