Tethered eh? A loved ones dependence is fairly common amongst a lot of people here, and honestly if you browse any of those posts you will see nobody really has a concrete answer.
On one hand, there is a concern of the effect it may have on the loved on, but on the other your own suffering presses you to find peace.
So the question is, are you willing to live for that other person(or people if multiple)? And when I say live I don't mean just aimlessly exist, failing to do bare minimum, since that merely exacerbates your suffering.
This is something a lot of us do, whether we are trying to push ourselves further into our depravity so that we finally find the courage to end ourselves or have simply just given up, it's not uncommon to simply just exist without intent.
That being said, if the idea is to live for another, then you can't simply do just that. To some extent you must try to recover and even prosper. Otherwise your simply sustaining and gradually worsening your suffering.
Now under no circumstances am I saying it will get better. Heck, I'm alive only because my mom is equally is ill and would most likely kill herself if I went. And from my short lived experience so far it seems to only progressively get worse each year.
Ultimately, I'm of the belief that we know when it's finally time to go. If you truly feel hopeless in your battles then regardless of tethers you will go. Maybe the best advice is to stay alive, or hold on, but it's genuinely really difficult to say in this current world.
The "correct" thing you "should" do is try to have a conversation with him where he does his best to see from your perspective. The main issue with forums like these and the normal members of society is the disconnect in the idea of death. Here, suicide is seen as a somber positive, where to the majority it's seen as cowardly, horrific, criminal, and to some a moral affront.
Honestly though, sometimes it's just best to go without saying much. Heck, sometimes leaving a letter grounds you to the people you're writing to and keeps you from action. My friend went out this way, and honestly I live with the guilt that I failed him. It's cold, and maybe they will never accept it, but maybe it's for the best. Hurts like a motherfucker tho if you wind up being the sucker who cared for you.
Whatever the case, and whatever route you go I wish you the best. It's very noble to live for another person. I think most of us, and most people in general would rather die for someone we love than live in suffering for them. So, on behalf of them, and to anyone else who is living for another, thank you.