There is an “imprinting” that goes on with one’s first partner, both for men and women. This is a God-given bonding reaction. This is why the “puritanical idea” of being a virgin at marriage and not committing adultery is actually a good idea, if you want to stay married and have the best possible sexual experiences.
I also believe that people seem to lose a piece of themselves with every partner that they have. If you have ever seen a old hooker she usually looks 20 to 30 years older, it's as if each new partner took part of her life away.