No advice. What would the point be? For every person advising you to retaliate, there will be someone telling you not to retaliate.
There is a quite interesting discussion group elsewhere on the Net:
http://www.experienceproject.com/groups/Live-In-A-Sexless-Marriage/332
There are some 40K+ user accounts associated with it, although I am sure many are not genuinely associated. Alao, the name of the group is somewhat misleading; it isn't just about people who aren't getting any at all, but plenty of people like yourself who aren't getting it as often as you would wish. Og getting it, but perfunctorily. Have a read. It probably won't give you any answers, but it might provide you with a wider, deeper insight into your predicament.
The problem with this sort of issue and the discussions that take place about it is that you rarely ever hear from those on the other side of the equation. That is, those who don't see that there is a problem, or prefer to figuratively stick their heads in the sand about it.
There are many common themes that keep cropping up, such as in the end it is usually not just about the sex, or the lack of it. It usually involves wider personality traits or characteristics. You shuld just read as much as you can, until your eyes want to pop. And of course there is some horrific dross and trolling.
I might only tentatively suggest a couple of thoughts. One, reflect on the process that has got you to where you are now, rather than think of how you fix the problem in terms of where you are now.
The 'why' really is important, although you may finding out what it actually is may completely elude you becuase it really might all be all down to him. Having said that, you need to be brutally honest with yourself. For example, could you ask yourself the question, something has changed from satisfactory to disatisfactory, or has it always been disatisfactory and you full well know it?
The one thing you can be certain about is that if it has to change, then you must assume that it is you that will have to change. He might well change, but the probability is that he will not. You cannot rely on that.