All right. As a man who was in that EXACT situation a few years ago, I feel compelled to respond. First of all, if you market it towards men, you're going to have to help make them feel like it's not their fault. I know that I thought I was doing something wrong in the relationship and it very well may have been (though I haven't had any complaints in my current relationship). Marketing it towards women is going to be more difficult, IMHO. I would think that they are looking for something that helps them realize WHY they don't want it and that's considering that they actually have a desire to fix the problem.
If this book came into my hands, I would probably read it. However, if my (now ex) wife wasn't interested in having sex with me, no matter what I came up with or learned from your book is going to help me. So, may I suggest going about it as a couples book? Give something for the men to practice, give something for the women to practice...or something like that.
I guess what I'm trying to say is that you can't pigeonhole something like this. It's a rather touchy subject (I once had a frying pan thrown at me when I brought it up), so you have to make sure that you're not attacking either sex. I've read some of the books and they tend to blame one or the other. But, if you manage to aim it towards being a mutual issue, it will be better served.
As Wayne said, however, it's ultimately the publisher's decision. If they don't like it, you'll never get it off of the ground. Now...on to your questions.
- Do you think it's enough of an idea, that there would be any interest?
Yes. I think that if it is written in a non-accusatory manner, it will.
- Do you think it's unsellable since I'm not a professional in the field? (I am a licensed MSW though).
Sincerely doubtful. But, you went through this and are willing to share your experiences with others. Does that not make you a quasi-professional?
- Should the target audience be men or women?
Both.
- Do you think the structure of it makes sense or is appealing?
Yes. There are a lot of people out there who want to 'fix' their sex life, but don't know how to go about it.
- Do you have any ideas for me to find a writing partner or crit group? I feel like it's kind of the same as Erotica writers. It's harder to find somebody to work with.
First, try meetup.com or something along that line. A lot of people have trouble finding people to be beta readers for their erotica, but you always have the AW forum in the worst case scenario.
-Anything else?
I wish you the best of luck and if you get published, I'm sure you'll save lots of marriages.