I have a sexual disorder..?

Hi, I'm a 23 years gay guy and I can't cum in front of other guy. Had no such problems with girls. I don't even know how to call it. Shyness? Sexual disorder? I always feel uncomfortable when I cum with a guy, sometimes I can't, turning off lights or covering my eyes helps a bit, I cant masturbate together with a guy, but when I masturbate alone (to gay porn) everything is ok, I mean its not about that I don't accept myself as gay or something, I've been sexually active as gay since 16, and it has always been that way. What is this? How to overcome it? Did anyone feel/felt this way?