It may be projection, on my part, but what I read here seems to describe an internal argument that you have with your husband, which may seem to get resolved on the surface each time, but which remains unresolved internally at least on your part.
What I write below is not to bash you. I spent 4 years in MC, and our counselor, a very kind and intelligent woman, had to really work with my wife on her perceptions because of her FOO issues and her codependent and secretive behavior.
"Pot" that you can get, with minimal risk, he may see as much riskier as he looks at his kids and his wife and thinks of "what's the worst that can happen" (one of my childhood friends found that out, he died with a bullet in his head over a little pot, left behind a wife and a fatherless child). You view it differently. Sounds like you still view it differently. From what you write it sounds like he and you came to a conclusion with the palliative care doctor angle, but you are still obviously stewing over it.
Does he know that you are still stewing over it?
Then, there is the affair, which he doesn't know about, and which colors every conversation and disagreement you have. Are you sure, when you are in disagreement, about anything, and he is irritated or angry, doesn't matter what it is, that you aren't standing there thinking "if you really knew what I'd done you'd really be angry".
From what I've learned, in 4 years of MC as well as in 30 years of professional practice, I'd be inclined to believe that you are involved in an invisible power struggle with your husband, that he may not even be aware of (or if he is aware of it he is not aware of how serious and deeply it runs) so he simply cannot understand you and your positions and where you are coming from.
You cheated on him with another man, this is not truly a secret, others know, but it is hidden from your husband. He is kept ignorant.
Others know. Think of the position it puts him into. Go onto the BS postings and think about what it is like for the perceptions others have of your husband when they know that he is clueless that his wife betrayed him. How could he be clueless, "trust", suspicious untrusting people are never clueless...they have clues all the time and we call them paranoid and fearful. Trusting people are laughed at behind their backs by others, and I've witnessed that behavior by men who laugh when they talk about how the f----- someone other guys girlfriend or wife and the spouse or partner doesn't know about it (never mind that these are some of the most messed up men I've ever known who have really awful personal lives).
resent me for being willing to break the law & put our family at risk
What is his job as a father? To protect his family, first and foremost. What is your job as a mother? To protect your family, first and foremost. Not to relieve your relatives suffering, she has doctors and nurses for that. I know, I've been through that more than once with family, and doctors do actually know what they are doing particularly today with hospice agencies and hospice nursing. They don't need you to put your family at risk.
Yet, you indicate that you are willing to put your family at risk, and have already done so in other ways.
I can't conceive of a way to bridge that gap
Perhaps that is where you should start, perhaps that is the problem.
I value intellectual connection, debate, all that, and I can't get it at home very often
No, you don't. You have lied to your husband, cheated on him, conceal things from him, and continue to engage in that behavior with others to his detriment.
You have said as much, you can't be honest with him, open with him, or the marriage ends. By doing so, you are manipulating him with your behavior, to protect you from the consequences of your own actions. You are not protecting him, or your children. You are protecting yourself. Dishonesty in the marital relationship affects the children in ways you can't imagine.
I will do anything in my power to help ease her suffering
That is not constructive behavior for someone who has higher priorities, namely the safety and security of your husband and children. That is what is referred to as Knight in Shining Armor behavior.
Opposing world views don't cause disconnection or irreparable harm in marriages, dishonesty and deception do. You will never get that "connection" unless you are willing to engage in constructive relationship struggles that ALL relationships have, in an honest and open manner. If you color that with secrets that you know will end the relationship, then you are manipulating the other person into staying, not letting them make the decision based on the truths.
Good luck, but there is no way this ends well without honesty, openness, and willingness to talk and letting the other person be free to make their own decisions.