Don't give up on getting what you want in this life.
It's just a guess, but I worry about two things others have mentioned -- depression, and "something happened". Whatever it is, it seems he owes you some sort of explanation, so don't let him make you feel like you should settle for his evasion of the truth of what is going on.
I hope you have the option of seeking professional help. Keeping it bottled up inside, if you do, is a waste of your life. It would also be good to have a professional assess the likelihood of depression.
Sorry if I missed it, but how frequently do you have sexual relations with him? Is there any sort of affection -- hugging, playfulness?
Also, have you tried talking about it with him when you are feeling relatively good? Or, is it always when you are feeling the worst of the despair?
