I don't see big differences between relationships and friendships. If you're one of my closest friends, I'd love to sleep with you and talk to you everyday and walk with my arm around your waist. I never admit this to people, because I fear their reactions. But honestly, I feel no drive for monogamy except the desire to add more security to the situation, make it clear that things are long term. I'd like it if all my close friends would have sex with me, and hold me through the night, and let me kiss them in public.