woman's main sex organ is her brain.

Ahh..sex drive. I do not know ANY women who have a higher sex drive than their male partners, and all of the couples I know--and I mean ALL--are experiencing the same thing. You are having a LOT of sex compared to most of the women I know (with and without kids), who are lucky if they have it once or twice a MONTH. I don't know what the answer is. People are tired, exhausted from energy spent on work and/or kids, stressed about the economy, traffic, you name it. Sex is just not as exciting after years of being with the same person, no matter how much you love them or are attracted to them. It just gets a little more mundane, in my humble opinion. Would love to hear from others on this, but this really is the most common complaint I have heard between married or long term hetero partners.
Almost Sexless in SF....I have some long held beliefs on this topic: First of all, I believe a woman's main sex organ is her brain. Unless there is some mystery left in the relationship, it is challenging to muster up any kind of drive for sex. I applaud you for mustering enough drive to have sex with your husband twice a week! I think that marital relationships have a natural course. The desire for sex naturally wanes when the routine of family life takes over. Most people have to really work at it to maintain a semblance of mystery which stirs passion-- whether it's fantasy, toys, porn, alcohol, oysters, chocolate, etc.
As for your husband's drive, I would suggest he satisfy himself on the ''days'' that you aren't in the mood. Obligatory sex is not fun for either party. Though, I've heard that it is good for a marriage. I, personally have a really hard time going along with it for my partner's sake. Others don't. It's an individual thing.
Tell your partner that the reason there was more passion when you were first dating, is that there was still mystery! You each put each other on a pedestal and were still discovering things about each other. This creates an element of surprise which fuels passion. Why does the story go that the girl always is attracted to the bad boy? Because it's the taboo factor. We want what we shouldn't have. Hence, there is attraction.You are being too hard on yourself - yes it's possible that you don't desire him ''every day''. And, yes, you can have beliefs of how a mother and wife are different because they are! You have lots of other emotional ties in your life. It is different than it was when it was just you and he.
This is a female point of view.