You already know that I think it is a good idea. I wouldn't talk to him about it, I'd just not take his calls. He will figure it out for himself. Remember he is 40, not 4.
Help him, by allowing him to help himself.
You have going thru this stress for 20 years, if you don't set your bounderies and stick to them, you will end up destroying you. You have a husband, another son and grandchildren. They need their wife, mother and grandmother, if you don't do it for any other reason, do it for them.
Love,
Dolly