A127---I agree with recovery2---I also think that it is important to remember that sexuality is a very complex subject--there are (can be) many, many factors involved. The factors are also very inter-related to each other. Sometimes, it takes professionals to do detective work to figure it out!!
But, it is always disturbing to the individuals affected. (men often deny and blame it on anything they can). I can hear how deeply this is affecting you--you are even "blaming" yourself. It is important that you are addressing this--as the internal misery you are feeling is not likely to "go away" o n it's own. Personally, I think it is a bit much to expect a satisfying sex life in a relationship in such turmoil. I honestly, don't know what your answers are--but, the important fact, I think, is that you are in an unhappy marriage (at least, at this point).
This is not because you are an unattractive person. Don't internalize the blame I say: Search for the root cause/or causes for your unhappiness.
sincerely, dandylion