You may be right. It may be his fear speaking-- but nonetheless, he obviously is scared by emotion , your needs, and loss. It is a good sign that he was willing to work on the relationship and the two of you gained ground and had a positive period. But your relationship will never be stable if he can't learn to reach out to you and love you even if you are stressed and sick.
This sounds deep rooted - so I wonder if you could get him to some couples counseling. He needs to talk about what makes him withdraw and what he- and you- can do to make this a less acceptable response to change, sickness or sadness. You seem to have been a good model for him- ask him small acts of kindness ( doing the dishes etc) and see if he can do them. Lavish praise on him- and try to show him the plucky side of you when you are having problems. You don't have to deny them- just try and take part of the time to take the emotional pressure in the room down a notch.
I do think you two could benefit from a professional therapist- if money is an issue, and it usually is, try and find a liscensed social worker- they are usually a bit cheaper ( but not any less talented) than psychologists and other professionals with a PhD. Your local church or hospital may have someone to recommend and it may even be included in your health plan. You can say it is about how to manage your health in the relationship and communication over those issues- and he might agree to do it on that or some less overwhelming idea than "the relationship". Good luck!
he needs to grow up and support you though all of this. it seems like he is a very me me me person. and it has been going on for a long time. I would lay everything out on the table and tell him how you feel about what he is doing to you and a therpist probably wouldnt hurt.
has he always been like this, meaning the whole 20 years together? or a new thing?