I know just how you feel, lossoflibido - my dh makes me feel as if there's something wrong with me, because I have little or no sex drive. It's been like this for years - there's always been an imbalance between our sex drives, and mine has declined since I've had the children.
I don't know if it's due to my depression, my antidepressants, my weight, my tiredness or whether my libido has simply run out. I just know that I feel the same pressure as you describe, and that pressure makes me tense and stressed and therefore even less likely to want sex.
In answer to your question, I guess we have sex less than once a month. I can't help feeling that dh believes deep down that I'm doing this on purpose, and if I wanted to, I could just change how I feel, just like that.
He percieves sex as affection, and says he doesn't feel loved if he doesn't get sex, whereas I want to feel loved and respected by him - he upsets me a lot (he has zero empathy or people skills, and I get a lot of the flack even when it's directed at other people), and I feel he dismisses my views and intelligence as not worthy of his regard - and he fails to understand why all this puts me off sex with him, even though I have explained it 'til I'm blue in the face.
I wish I could be more positive and tell you something that will help you sort this out, but I hope it helps to know that you are not alone in this.
[un-mumsnetty hug emoticon]