Ya. I'm in the same boat sometimes. I want it way more than she does. We learned and got better at it. It still recur rs but now we know what to do.
We found out it was a combination of two things. One was we were not setting enough time aside for it. Who wants sex when their mind is on something else all the time? Two we were not having enough fun as a couple. I mean we weren't going out, weren't indulging in anything remotely pleasant and were not talking just to hear each others' voice anymore (hashing out where the kids' college money needs to go and how much isn't really pillow talk). In short we were letting too many other things take higher priority.
There's this TV show in England (I think) called the Sex Inspectors. You may be able to catch it on cable somewhere. I thought it was pretty good. They talk about sex a lot but, at heart, it's really the same message. Good sex comes from a good rapport with your spouse and a happy you.
I still want it more than she does *sigh* but what can you do?
We both try and its a ton better than when we didn't make it a priority.