I know how you feel. I know my husband loves me, and me alone. But sometimes, in a weak moment, the worst thoughts come into my mind, and I cannot control the impulse that he's with someone else.
I've talked to him about it, and we've worked together with a therapist to find ways of keeping me reassured. I have to admit, it's incredibly selfish on my part, and equally generous on his part that he's willing to let me know where he is, what he's doing, etc whenever I ask. I do my best not to ask, and can sometimes go for quite a while. The fact that he was willing to be open about the people he deals with helped me to be reassured.
I cannot stress enough here how lucky I am to have a partner who understands my fears and is willing to deal with them in a way that gives me, when you think about it, a lot of control over his life. My part is accepting what he says and not flying into a fit about it. It's a delicate dance, but it has worked for about 11 years. I hope this helps.