You have no kids together (I assume). You're not married. You're not satisfied. What are you doing? This doesn't get better. Ever. It doesn't matter if he's stressed, working shifts, working out or the thousand other excuses he'll have for not feeling up to having sex. He's breaking promises now? If you marry him, his ultimate promise breaker on the sex issue wll be "you knew I was like this when you married me."
This is not the man for you and you're not the woman for him. There are women out there who want less sex than you do. And let's not pretend this is the only good man on the planet. There are other great men out of there whose desire for sex matches your own. Take your attractive self out there and find one of those. Do not marry the one you're dating. The point of dating is to get to know the other person. If you're interested in getting married, you're supposed to take this time to figure out if this is someone you could live with for the rest of your life. You already have your answer on this one. Don't try to make this something it isn't. I don't deny you may have strong feelings for him but if you're feeling sad and rejected now, imagine how you'll feel after you're locked in.
Break up. You can't change him. (You can't change anyone. They have to change themselves.) You shouldn't try to change him. There isn't enough lingerie, counseling or favors (?) in the world to justify trying to make him into something he isn't when you could just walk away and let him be himself.
I think you were hoping for another answer but I honestly think this is best and, in the long run, easiest.
Sorry for what you're going through. It's a VERY common scenario on this board.
This does not bode well for your relationship. It's one thing to lose the desire for sex, another to stonewall your partner's efforts at getting information. If I were you I'd shift the discussion toward this problem. Tell him that you don't care what the reason is, but you need to know, before you even think of committing to him, what's going on. If he's unwilling to keep you in the loop, I'd strongly advise against marriage.
I agree with the other two posters.
"I think you were hoping for another answer but I honestly think this is best and, in the long run, easiest."
Looks that way since she erased her post.