I don't think I'd have much of a problem having sex with my closest friends. Each of them is very dear to me and I happen to find them very attractive. Maybe it's because we in our own ways complement one another. Maybe it's the bond of trust between us. Maybe it's the fact that we look out for one another and there are just few enough of them that if that level of intimacy developed – it would still be a closed circle and somehow so much safer.
My best friends have all the qualities I'd want in my lovers, and if not for the matter of them being paired off – I'd make this known.
One or two of this circle have already let me know of their thoughts and attraction. I joke that our relationship is borderline incestuous because we consider each other like siblings, with traces of mothering one another. To be in a safe and nurturing relationship is certainly attractive. One or two of this circle have already let me know of their thoughts. One filled with guilt after a case of heavy drinking. The other still close and they're still telling such in playful flirting back and forth though we no longer do anything about it.
I don't think I'd have much problem aside from the messiness it might cause and I don't think I'm so bold as yet as to say as much to those who don't already know I'd welcome such a moment. Perhaps the messiness and possible loss of that safe feeling is what worries me.