I get that, and one of my biggest fears in life is going through what's happening to you. I think about stuff like that every day, and try to push it back with "we'll cross that bridge when we get there."
Okay. That's cool. But then what?
I won't try to fix you with catchphrases or slogans or bullshit. I don't have any answers for you. I can say I feel genuinely sorry for you, but honestly, do you give a shit?
So all I'll say is this: Please try to find tiny victories wherever you can. You probably hate it when people talk about "fighting" cancer, but the struggle is mental as well as physical. Fighting means doing everything you can to not let it consume your identity. Fighting means making space to laugh, to feel joy, to have moments of "fuck it."
It's not easy. I struggle with this and I'm perfectly healthy. But it's your only choice. Your other option is misery, then death. And that's not you.