Should I trust him or not?

My boyfriend has this lady friend that he stays with. He sleeps on a blow up mattress in her living room and I come by there as I please but I haven't been seeing him quite as often. Anyways, when I did see him he had a hickey on his neck. He kept apologizing for it and saying that he was sorry and that she had came and got in the bed with him one night and was trying to have with him and he didn't want to so she bit him on the neck. I don't know because our life doesn't suffer at all. Every chance he get he is trying to have with me. I don't know if I should trust him or not I want to. But, then a part of me goes what if he is having with her. Obviously, she wants to and whos to say he is not fighting her off. But, he keeps telling me that he is not having with her and how could I feel like that when everytime he sees me he is trying to bolt me down somewhere. I want to trust him but I don't know if I should.