I really feel for you. It sounds like you are so desperate for more rest and to just find a little opening that might shine with the light of hope. I don't have an amazing success story for you.....yet, but I have a small success story that for us signifies a start towards weaning and hope that it's possible to do it gently.
My son is 31 months and has been a frequent waker and all night nurser since birth. To this day he wakes up just about the same as your son, 4 - 8 times a night and nurses back to sleep most times. I am exhausted and know my health has been affected, but I haven't been able to muster the strength to try anything big as I figured I wouldn't be able to handle any more loss of sleep.
However, now the success side of the story! I go to school on Friday nights and a few weeks ago I decided to tell my son that I would be home late and so he wouldn't get any milk until a while after he went to sleep. If i am in the house my son will not go to sleep with my husband (his Dad). When I'm gone my husband successfully gets him to sleep and when I get home he is usually still sleeping. That took a while to accomplish though. That was the first step though. Once he was able to go to sleep with my husband I continued to be the one to respond to his night wakings with nursing, but recently I decided that after getting home from school I would let my husband try going to him to comfort him. I thought that maybe because he went to sleep with his Dad he would be more willing to accept him for comfort. We tried it once and it worked. The next week before going to class I told my son that I would be home very late but that papa would be with him. It worked again and Dad was able to comfort him back to sleep on his first and second wakings. No crying!
So this is what has given me hope that full weaning is possible. I have realized that ultimately I need to be the one to wean him. He needs to wake up, have me respond, but not nurse him. This will be harder, but it really gave me hope as we tested the waters with just the right set up when I was out for the evening at class. It is possible for him to go to sleep without nursing. That's all I needed to know for starters.
Could you possibly try leaving the house for the late afternoon/evening and letting your husband do the bedtime routine, and telling your son that you'll be out for a little while but back just after he's asleep? Then make sure you are there for him when he wakes up the first time, but eventually try letting your husband do the first waking?
I wanted to say too that our son also cries very hard to the point of throwing up when he is truly upset. This doesn't happen often and it's never because we leave him to cry. He just has a sensitive system and this has happened a few times. It's such a horrible experience so just wanted to say that I empathize with you on that.
This is the hope I have to offer right now! Maybe it's helpful, maybe not, but I do wish you much luck in your own process.
I had hoped that by now, at 31 months, my son would naturally be waking less and wanting/needing to nurse less. That has not happened. I don't know when it will, and I admit that I just resigned myself to the frequent night wakings a while ago. My son is super sensitive and just needs more comfort at night. By letting go I guess I hope that will help things change on their own.
Hugs to you!