sorry Laurence but open relationships do work, I'm sort of in one myself and we've been very very happy for the last ten years. My wife does not believe that men are naturally monogamous, nor does she want a relationship whereby her partner is only faithful to her because he feels obliged. therefore when we got together she decided that she was happy for me to sleep with other women if I so desired, but she would not sleep with other men ( as she said if she wanted to do that, from her perspective our relationship would have reached an unsalavageable point). I found this a bit hard to get my head round at first ( she was guaranteeing NOT to be unfaithful, yet was telling me I could sleep with whomsoever I liked as long as I didn't form a relationship with them, so caual sex only).
Then it occured to me, that actually she was giving me permission to mess up or take our relationship to a whole new level. I've chosen so far never to have been unfaithful and as a result our relationship is solid as rock as she knows everyday that it's her I want ahead and above of all others.So just because you are in an open relationship, it doesn't actually necessarily mean that you sleep around, and it certainly doesn't mean that there is no love.
I'd be careful though Ophelia, as these two sound as though they have a evry special understanding and you could get hurt if you start to want a relationship with him, rather than just casual sex, and yeah men can tremble with desire :)