Did you respond to his "maybe later" about the book? That might have been a good time to insist on something that was important to you. You could politely say, "No, this is important to me. Unless you've got something more important that we need to do right now, I want to go get this done." The worst he can do is say "no," and it sounds like you hear "no" when he says "later" anyway.
I would caution you not to go off half-cocked thinking you can solve things by dealing with his mother issues. They are probably part of the problem, but just because that was the first thing he came up with to explain his behavior doesn't mean that it's necessarily as important as he thinks. My wife had and still has problems with trust and intimacy from her mother, but addressing them has not solved all our problems. It's not that I want to discourage you, but I don't want you to expect a climactic family discussion where you resolve his religious guilt over marrying the evil divorcee and then things gradually fall into place. I don't think that's the whole issue here. On the other hand, I don't think your mother-in-law is helping, even if that's what she's trying to do, and that includes lecturing your husband for you.
Your reaction to his climbing into bed to cuddle with you is exactly what I would have thought a year or two ago, along with resentful thoughts about how "I'm not your son or your father, I don't want to stop at a hug!" But while you can't avoid having the thought that "maybe he's just testing me," I hope you also think about that thought and realize that it's only one of many possible explanations. The simplest one is that he needed a hug or thought you looked like you needed one, and since he's been thinking about you more lately (clearly not enough, but more) he thought about it at the right time and had the courage to do something about it. That's important.
How important is this church in his life and yours, by the way?
