Wow guys, thanks so much for the thoughtful replies! Definitely food for thought. Will answer each point in order...
A) we discussed these issues. He is English and quite indirect about stating his needs/avoids confrontation. But he has finally been able to be clearer about what's been happening in terms of having a less adventurous sex life. A lot of this has been because I've apparently been putting so many rules and restrictions in place he has been feeling increasingly "caged in", controlled and unable to be himself. As he used to do in the past, he dealt with it through being withholding or withdrawing, but he's realising it about himself now and he's learning to express things as and when they bother him instead of only doing what he thinks I need to make me "happy", because he can see in the long term this way of behaving is damaging to both of us. So some things re my needs not being met are being resolved through this "letting go" process. Even where we are now is much more open-ended and flexible than where we used to be, and he is appreciative and happy about that.
B) I thought about this point, and I think it might be a hang-up from when we got together, at that point he wasn't poly-identified and had about 4 girls he was sleeping with, all of which thought they were his girlfriends. He would fill every night he didn't see me with a different woman without full honesty and I wouldn't be able to communicate with him much (apart from a cursory goodnight call). So it's a combination of being overwhelmed with a large amount of partners, lack of honesty with those partners and lack of ability to be there for me when we're not together. Looking at it now I can see much of it is part hurts and we've both made mistakes, so might be time to let that go. We've talked about it and he is reassuring me that if he sees his secondary more often I'll be able to contact him for chats when I want to - of course I wouldn't take advantage, but perhaps keeping in regular contact would help "normalise" the situation. He is also adamant that he's happy with the both of us and isn't interested in going back to having numerous partners like he used to, so this helps.
C) I completely understand, again this might be a throw-back to several of his previous partners who would prefer it if I didn't exist, got very territorial and weren't supportive of our relationship or respectful of my boundaries. So I became more controlling because every time a relationship progressed in the past it resulted in indirect pressures and manipulation. While this isn't the case at all now, I still think there's a difference between him having a secondary partner and a full "sharing" of him, so there's still a switch in ways of thinking I may or may no be able to do. Ultimately I guess I still want to control how deeply they become involved/how central she becomes in his life because I can only share so much, regardless of whether this is even possible. Sorry if it doesn't sound grown up! But please remember I'm not poly-wired so do struggle with this whole scenario. In all honesty I would prefer it if he was just a swinger, and I would prefer it if she had another primary relationship, but I also know I want them both to be happy and that they want me to be happy. I know they'd always consider my feelings and comfort.
Dagferi: that's helpful, and yes, I hope I get more comfortable. The fact we don't live together is I think one of the reasons I feel unsettled, as due to various complicated reasons it's unclear if it will happen in the future. I don't want to live along or with flatmates forever and he knows it. But me not being poly, looking for a partner who would live with me is likely to result in us breaking up... so there are still levels of commitment and lifestyle discussions to be had over the next year or two.
sparklepop: yep, you've hit the nail on the head. It is painful that no matter how much I give it's not enough. I didn't realise I was signing up to a full V so it is a boundary I feel is being slowly trampled on and I am powerless to do anything. It's not a good feeling. I want to get to the point of "sod it" and let him make his own decisions - I think I'll get there eventually - and he keeps saying I'll remain his primary, although I am starting to feel (especially without living together or sharing a life in a practical way) that it's just a hollow term. When I ask he isn't able to say what he means or what's the difference between the two relationships apart from us seeing each other more often. So perhaps it's the idea that us seeing each other much more often than them is literally the only things remaining differentiating the two relationships in my mind and protecting my "primary" feelings, which I do need to be able to cope (as I'm not poly). Does this make sense?
Re exhaustion, that's also a question... she goes to sleep earlier than us or him, and it doesn't sound like she's keeping him up all night; I wouldn't say he's been significantly more tired or less interested in sex with me after spending a night with her. It's also worth noting he has delayed ejaculation so without wanting to be graphic - it's not often that he'll be too "drained" to perform after a short while... these things do have their advantages
he does however work in a very draining job and comes home at 10-11pm during week nights. This is another reason I find weekends so hard to share...
But I think you're right, I should let us both learn and grow through this experience. We'll need to figure it out, but I might say we try two nights first and see how it feels without lifting "restrictions" completely. Or is this still being controlling?? We love each other very much and this isn't a major drama/crisis scenario, but it's hard to know exactly how to move forward...