One more thought: The bigger issue here for you is that your wife doesn't seem to be making much of an effort to find solutions to something that is causing you pain. It isn't as much about the sex as it is about this. Is that a fair assessment? If so, highlight that issue if you write a letter or have another conversation with your wife. Even if she doesn't feel like she can have sex right now with you, perhaps she will be more willing to take the first steps toward finding solutions if you present your need as being a need for effort on her part rather than a need for sex. This is then more about her interest in your relationship rather than her interest in sex.
