Interesting, all the work man goes through to figure out what they could've known millenniums ago if they had just studied the bible, ain't it? Sex isn't casual and was not designed to be treated as such. It's a physical AND spiritual bond between husband and wife...so by bonding with anyone attractive that will consent with you, you're taking a wrecking ball to your soul's capacity to experience true satisfying intimacy. So it makes sense that this same sort of thing would occur to the body as well.