Oh gosh! That sounds awful!
Me and my partner were like that for a while, but he had health reasons and it was literally too sore for him to do it. It took a long time and I got really upset about it. Like you, I even cried myself to sleep on a couple of occasions. It seemed so unfair because he wouldn't do anything, even just touching me. Getting worked up about it made it worse because of pressuring him, and trying to explain my needs to him ended in arguments. I ended up just calming myself down about it. Just got it in my head that we were one of those couples who didn't have sex. But I ended up getting excited about the prospect of the male masturbator sleeves and bought a Tenga Egg.
He could just lie there and have me do the wrk for him and he really enjoyed it. It breathed a bit of life back in to our sex life. I didn't think he would want anything to do with it, but he was really enthusiastic about it. But sex was still a big struggle for us.
It was only in the last few months I found dirty boxers covered in his cum 'hidden' under the bed. When he comes he suffers a terrible cramp in his hips. So bad that I would be crying in shock while he would be screaming in pain and not knowing if to get an ambulance or not! But these boxers under the bed that he had used to clean up with was concerning me. I thought he didn't want me and that for him, masturbating was better than having sex with me. I ended up confronting him on the dirty boxers. He didn't want to talk about it.
But the last couple of month, our sex life has been reigniting! We are cuddling more now, and snuggling in bed each night, we are talking more and being more 'couply' than we have in the last 2 years!
Turns out that those dirty boxers were because he was 'training' himself! He cares so much for me that he had been practising his stamina and learning how to orgasm without getting the cramp and pain! We haven't had the cramp pains since! He is lasting longer, he has more stamina, and our sex is much, much better now! Brill!
Thats enough about me though.
If your partner has no clear reason for his withholding of sex, then I reckon you should just ask him. Be tactful. Don't ask so that he knows you are asking about sex, but ask if he is Ok, ask if there has been anything bothering him. Try and have him open up. Just say you have noticed he has been a bit different lately and you are concerned for him.
Be nice to him. If you do all the work in sex, like giving him a blow job while touching yourself, things like that, does he mind or does he try to stop you doing it? Do you ask him to lie back while you do the work? Whats the response?
If you can't get anywhere after a couple more months with this, then it sounds like a dead end to me, I'm sorry to say.