I have lost one good friend by having sex with him. He was straight and interested. We had sex----and for about a year, we had sex constantly. Then, he began feeling guilty about it (He was married--as was I), and our relationship cooled. I told him we could still be friends and not have sex, but he wanted to not even be friends any more because of the discomfort our relationship caused me. Losing a friend was not worth the sex. Also, it was not the greatest sex I ever had. It was a real mistake.