Self doubt(help!!), How do i stop this self doubt that hinders my relationships?? Options

[Unrequited_love]

OK this has been driving me nuts for the last couple days and I wanted to know if you guys have any suggestions or advice on how to stop this. You see Im in an amazing relationship with a really great guy...hes never done anything to make me feel down about my self or make me doubt his commitment but no matter what i cant seem to shake this feeling of self doubt. Ive put myself into a place now that i dont see why he would want to be with me so he must be lieing and hiding something and its not fair to him or myself because now im sitting in a different city freaking out thinking that something must be going on in my home town because im not there and i know hes a better guy then that he would never do anything like that ever! its as if i believe because ive been hurt in the past that is destined to happen in this relationship and thats making it so that im pretty much sitting here and waiting untill it does happen so that i can just get it over with but yet when i sit back i can not see one reason that i can see it ending. the worst part is i know that im doing this and yet i dont know how to help and it affects him as well because if my mind goes into self doubt mode while im with him and i get all quite and upset then he starts feeling like shit to because he knows im upset. I know that my mind being in this state will just end up ruining my relationship so what do i do about it so that it doesnt? The last thing i want is to loose him.