Hello, Marine_Wife. I replied on your post in another thread as well, but your question is a little different here, so I wanted to respond here, too.
I think the guy is feeling pressured and that is never good for a guy's libido. I think the spontaneous thing is his way of saying "Don't let me know it's coming so I don't feel pressured" tho I'm not sure.
Try sitting with him and letting him know that you aren't trying to get sex right now, but want to talk to him about it. Let him know that you really enjoy the physical intimacy (and it never hurts to tell him it's cuz he's soooo good at it

But you don't want it to become a forced thing. Let him know you are happy with any affection you get.
My guess is he's feeling pretty insecure right now. It's confusing for a guy (especially if they aren't that experienced) to have a lower sex drive than the woman he is with. Let him build up to breaking the pattern.
Also, let him know it's okay for it to be all about him sometimes too. I used to worry that if i needed a quicky, she was going to be disappointed if I didn't make it wonderful for her, too. Honestly, I never got over that, but I'm with someone else now. Tell him the next fantasy that pops into his head is okay ... anytime, anywhere, no matter if you get off or not. It's all about him and what he needs. He just gets to repay the favor sometime
Hope it helps at all. It's a tough problem.