I realized that I was holding my breath the entire time reading your reply! My heart just goes out to you because you’re in an untenable situation with your husband and his decision to not continue treatments which could potentially give him many healthy years.

Obviously, this is his life and his personal decision to make. But it certainly doesn’t feel fair to you and his decision is leaving you in a very helpless state. You’re wondering what to expect and how to help him. Honestly, I’m not sure there is much you can do to help except to be supportive and to listen. He has made his choice so it’s futile and frustrating for you try to change mind.

Because his blood cancer and other health issues are continuing to advance, to put it bluntly using his words, he very well may die tomorrow. He is in an unpredictable health state and there may be a health crisis/event requiring an emergency trip to the ED.

Now is the time where you two need to have frank discussions. You might start by telling him that you won’t push for doctor’s appointments anymore and that you finally accept that he has made his decision. So talk to him about what his last wishes are for end of life care.
Does he have accounts in his name with passwords you don’t know. Are all the documents current for Power of Attn for health care in order? Is there anything you want to ask him…because once he’s gone it is too late. Again, I’m sorry to be so blunt. But my husband and I had to face all of this 5 years ago when I was critically ill. It’s amazing the things we thought were in order, weren’t! So now is the time to have those uncomfortable conversations. They become easier once the ice is broken.

I found several good sites regarding end of life discussions that may be helpful for you. They’re thought provoking but may help your husband understand the gravity of what is happening.
https://www.joincake.com/blog/end-of-life-questions/
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https://www.aarp.org/caregiving/basics/info-2020/end-of-life-talk-care-talk.html
My fellow mentor, @pmm, had some very good suggestions in this reply for you. I’m wondering if you saw it. Here’s the link. https://connect.mayoclinic.org/comment/1069438/

Do you have friends or family nearby who you can talk with about any of this?