Many men experience the idea of their wife having sex with another man as both threatening and stressful, but also somewhat arousing as well. It’s an intense physical and emotional state.
I think the sense of threat and stress is easily understood by most people, but the sexual arousal is not. The source of the sexual arousal comes from the natural
sperm warfare reaction. If another man is putting sperm into your wife’s vagina, one very biological method of trying to ensure that his sperm does not impregnate her is to flood her vagina with your own sperm. The human penis is also designed to work as a suction pump when thrust in and out of a vagina as well. So having watched another man ejaculate into your wife, the immediate best reaction to seek to avoid her getting pregnant to him, is to put your penis into her and vigorously have sex and pump his out. Plus of course dump a large as possible volume of your own semen into her. Hence the huge sense of being turned on. Even when used as a fantasy the sense of “cumming unusually hard” is experienced.
