I'm sorry you're dealing with this. I recently lost a dog to cancer and have also, longer ago, lost one to Cushing's. It is always hard. With one exception, every dog I've lost has been euthanized, and with only exception, looking back I have thought I waited too long to make the decision (the exception was a decision made either at the right time, or too early -- I don't know which. The thing is, of course, you want to euthanize them once they are to a point where they are suffering and then, ASAP, but it's hard to know what is temporary and what is long-term and they won't recover. I find this is often true even with chronic conditions like Cushings.)
I have also noticed between me & my DH that our own views/values about end-of-life and quality-of-life get played out by our animals. My DH is more of a "seek treatment / endure" person and I am more of a "end the suffering" person.
I think we generally know that dogs mask pain/discomfort/illness, when they can, as they are social animals that are predators and vulnerable to attack by their pack mates, if they are feral. There are exceptions, but of my own I think most endure A LOT before they start to complain.
I don't know anything about the division of labor in your household, but agree with others who have commented that given the situation and difference in opinions, it looks like your DH should be dealing with some of the care/cleanup problems.
And I, too, am sympathetic to the thought that there are young, healthy, friendly dogs being euthanized every day. The reality is, there are. So paying big bucks for one dog rather than helping another is a hard thing to justify. At the same time, like most of us I get (very) attached to my dogs and am willing to pay for their comfort (good palliative care) and treatment, if it will likely prolong their lives by a noticeable amount (without damaging its quality).
In short, I don't know -- and I see arguments on both sides. Your husband's views and your relationship with him are also important (I definitely delayed euthanizing 1 dog because my DH wasn't ready, and would have done anything for another [but nothing could be done] because my son wasn't ready to let her go), even if that means (within reason) honoring a decision to nurse your dog along for awhile. Good luck to you in finding a good path, and to each of you as well as your dog in his having a comfortable and peaceful final few [days/weeks/months -- whatever lies ahead].