This is gonna be kinda hard to explain, not by embarrassment. More of just, I don't know. It's really kind of fucking weird. I'm a straight guy, in a relationship for about a year or so but I've noticed I can't get off during sex/masturbation/ect unless I'm thinking about another dude having sex with my girlfriend. It was never the thing before, I only started to realize. At first I only noticed I was doing it when it was just me on my own, enjoy myself with myself. I'd see these dudes she used to talk about, or kinda had a 'thing' with, or basically cheated on me with with her. Having their way with her and it's the only way I could get off when I would masturbate usually. Then I noticed a couple of times it was the only way I was able to cum during actual intercourse with her. I really don't know if this is just a really fucked up kink I'm having or a problem I should be worrying about. It kinda bothers me, anyone ever hear of something like this?