That's my situation exactly. About two years ago I had both a husband and a girlfriend. I never felt more complete in my life. The inevitable happened and she couldn't handle sharing. Both of us agreed from the start this wasn't going to be a real relationship, but it got out of control. My husband encouraged me to go for her when I told him I was attracted to a woman I worked with. He was able to keep his jealousy in check, she wasn't. The three of us had an unofficial contract, so to speak. She had me overnight one night a week and for a long dinner another night, I was his for the rest of the time. Established boundaries and firm agreement between all three made it easier for a while. She broke my heart. My husband never had a problem with my love for her, but it was hard for him to understand my pain when I lost her. I don't know if I'll ever do it again. I don't know if it's possible for people to be in that kind of relationship without someone getting hurt.