I and my young adult children cared for my husband through stage 4 bowel cancer, until his peaceful death at home. So I do understand the kind of support that you're going to need, and empathise with how you're feeling. But at the same time, I read this...:
He has been an absolute rock for me over some very difficult times, the death of my parents, divorce and now this. He keeps my spirits up and provides a lot of emotional support
.. And thought, 'poor guy'. What kind of a young adult life has he had, having to prop you up, while grieving his own losses of grandparents and his dad (presumably) moving out? And now he's expected to care for you as your illness progresses/your chemo takes its effects.
He sounds like an amazing person, but really, no-one should have to live their twenties that way. And he works full time, so I'm not sure how he's going to be able to continue doing that, as well as having a social life, while carrying for your increased needs.
You really need to start having some outside support, even if it's just for an hour or two a day, to get you used to it. And I'm afraid you have to give him his freedom.
I sometimes wonder what will happen to me should I get similarly ill. The experience would be very different from my husband's, as I live alone, whereas he had me and our 21 and 22 year old daughters at home. But that's the way it is. And I wouldn't want the DDs to go through that again. They need to work to pay their mortgages, and one of them has my grandchildren. It's just how things are, and if it happens, that's my problem.
Let him go.