I Don’t Trust Anyone?

Ok, I’m 28, I am in a wonderful relationship, I love my boyfriend more that anything, I know he loves me very much,. I have really never trusted anyone in my life (friend or boyfriend), I am always on guard that I am going to be lied to or cheated on. My boyfriend and I have talked about this and he said he can deal with me being a jealous person, but I am afraid he won’t be able to deal with it, I do not want to loose him, I trust the man with my life, but how can you trust someone with you life and still be on guard about lieing and cheating??
How do you trust people?? How do you know they won’t lie or cheat, I know you can’t know 100% but what if they do, I know you can’t stop something that will happen, but how do you put your mind in rest? So many thoughts go through my head, and other days I know he would never do anything. I’m not sure if I make things up in my head or what. I probably sound crazy, but I need answers. Please give me some advise, thanks….Dee