Sometimes I go from 1 to 2 hours pounding and don't cum, I manage to keep my dick hard the whole time and it usually turns out to hurt me and my partner, sometimes they get there and lose the heat before me, so I need to masturbate to do it, and it have happened that even masturbating I couldn't do it. Any advice for something like this? I cum normaly when I'm with myself. (sorry for the bad english, not my first language)