Please girls.. why?

I don't know that he has ever been cheated on but I know about some shit that he's told me about...the thing is that he does not really know if what he thinks went down, actually went down. I have had many relationships. I have never once cheated. Nor have I ever given him any reason to think that I would. I think that he has some kind of old fashioned values or something and he just does not think it's right for his girlfriend to be hanging out with other guys. He opens car doors for me and things of that sort. And my brother is the same way. He told me that he did not blame my boyfriend. His girlfriend is not allowed near other guys either.