Yeah, I agree with Mimi, I think you are the one who can't be just friends here. When I was single I always had mostly guy friends and my best friend was a guy. The only times it was a problem was when one of us wanted something other than friendship. Maybe you can get past that, maybe you can't, but you can't be his friend in the hope that it will turn into more: you have to be his friend for the sake of being his friend, not with some extra expectation. That isn't fair.

(My best guy friend dumped me when he got married. His wife did not believe we had never fooled around and would not do so in the future. I told that to my husband, who had never had a problem with my friend, and he said, "Wait, you guys weren't fooling around?" I am married to the least jealous person in the world.)