Turtle, I dunno if this counts as crazy, but I've had a threesome with my ex-girlfriend, and my boyfriend. Now this is probably making me sound like a slut, but I'm really not. I'm a good middle class girl, ok so I like to tease and flirt and I like to a bit adventurous, but I don't sleep around. The vast majority of my sexual experiences have been with people I know really well or love. My ex-girlfriend is my best friend ever and I love her loads, but it became obvious that I wasn't a lesbian and was bisexual.
Anyway, to cut a long story short. My BF wasn't allowed to touch my ex-GF. My BF was happy for me and my ex GF to do our thing, surprise, surprise! It was early in the relationship and I think he just wanted to have a threesome lol! So with the rules in place it was nothing like a porn threesome, but it was good and we all enjoyed it. After the event though it's emotionally difficult, especially if you have strong feelings for both of the other people involved, like I have.