Thanks for your reply Sparklepop, it's reassuring that I'm not in a situation that's very unusual!
I think that the fact it's a new situation is definately a big factor. She's had sex outside our relationship once before this (and this wasn't discussed/agreed upon beforehand) and has fooled around with a couple of friends a few times, but this is the first time that she's had sex with someone else, spent the weekend with them, and the first time i've wanted to hear all the details. I'm torn about wanting to know the details of future encounters - I love to hear what she's been up to, and when she's all happy and glowy like that, she wants to share!
I'm not sure i explained myself right about the intimacy.... P is my primary partner, so we do have a lot of intimacy between us. I guess I feel more threatened by her sharing intimate moments with others than I do the sex. She gets something from them sexually that i'm not able to give (the logic in my brain says), but she can get intimacy from me, so why would she want it with someone else? I know it makes no sense, and even just sharing on this forum here is helping me to realise what things I am feeling. Sometimes when we look closely, we realise how rediculous our feelings are.
I'm not sure how i feel about not being able to have sex with other men. I'm definately envious of the freedom P has, but I also understand the reason B feels that way, and he has said he is happy to slowly explore it (beginning with things like us going to a swingers club, so he can be involved). But to a certain extent, if i had that freedom, I know I would probably have to face up to my own insecurities/shortcomings - maybe it's nice to have B as the reason I dont do it, than knowing that it's something in me stopping me doing what i want.
It's good to know that this is normal and i'm not totally failing at poly/open relationships! Looking at it logically, I know i'm reacting so strongly at the moment because i have been neglecting my own need for other people - for friendship as much as anything else. I've realised that that is an issue, and I am taking steps to address that.
The more i type, the more issues it sounds like i have!! I've been putting a lot of work into my relationships, and my work recently, and I think i've been neglecting myself a bit, and having a lot of realisations of things that should have been obvious at the moment!!