Help with my relationship?

I really love the guy I'm with. We are currently in a long-distance relationship and we've had a lot of issues in the past. I want nothing but to make it work for him. But I can't shake the feeling that he's lying or talking to other people. when I talk to him about this, he tells me that he wants a relationship with me, and that he isn't. I feel stupid and paranoid but I keep on bringing this up to him and he's getting frustrated with me. Is there anything that I can do to get rid of this feeling, so I can stop being so paranoid. Has anyone else dealt with something similar.?