I think when you are in love you can reach an emotional high during sex that you cannot achieve with someone you are not in love with. Intense emotional feelings shared between two people can take sex to an entirely new level. I know this because with my g/f and me, we have experienced incredible satisfaction with each other, the likes of which neither of us have ever experienced. Sex without love is ok, I have done it before, but sex with love, especially intense love, is a feeling that just cannot be described until you experience it yourself.