If your man told you one of his fantasies involved large Penises, would you stay with him?

As you said yourself you have bi fantasies. I don't think it's much different then that. We all have fantasies, and a lot of times they involve the same sex. I would definitely stay and to tell you the truth I would feel happy that he was comfortable enough with me to be open enough to tell me. He took a big risk in telling you, so don't dash that trust by turning on him with it. And who knows, maybe someday it can find a way into your bedroom and you might find it a major turn on!