It sounds like your life is not unlike mine, only what's happening to me in my 60s is your experience in your late 20s. Still, we're both human so maybe we can help each other.
I'm just now adjusting to being able to go do things on my own, as my wife's cancer is in remission. The after effects are still very strong - I get what you said there. It isn't easy, because most stress management strategies that would work for me involve travel, and I am not doing that. I stick around because I'm often needed.
I cope with stress by seeking activity. Since I need to stay around home, much of that is mental. I need to become engaged in things, even mindless things. They're vacations from the day to day. Having a lot of fishtanks and engaging in the detailed, busy world of breeding killifish is great escapism. It won't change the world, but it will put me into tiny situations where if I don't figure things out, they won't work. They make me "do", with a flexible schedule and a lot of puzzles to solve. I have a friend recovering from breast cancer who uses gardens and houseplants in exactly the same way.
I have other relatively mindless activities - a weakness for watching baseball or hockey - I used to play and coach, but now I quietly over analyze them. I have an old dog who keeps me busy, and I walk as much as I can - moving to a new environment close to the ocean has been a great thing. We can sit and worry, especially when we have a lot to worry about. When I go for a walk, I try to break any thought patterns that would have me brooding on the negatives. I'm not an optimist, but these things don't have to be extremes. I try to cultivate my inner dog, and get as immersed in the environment as my lousy human nose will let me.
I have a murder of crows in my yard who are training me, and I enjoy trying to figure out their social dynamics. Air fish. I watch air fish now too!
This may sound harsh, but I have learned that for me, stress is a control problem in many situations. I have no control over events around me - if I did the world would be a different place! If I seek to control my world, it's a guaranteed stress situation because I will fail. I live in a web of other peoples' lives, decisions and health, as well as my own. For a long time, "me time" was stolen time, and even something like fishforums was a good thing when I was on duty and ready to respond, but when things were quiet between 'calls'.
My fascination with the natural world has been a great help. I read a lot, keep learning a lot and looking for things to engage my mind that are not related to cancer or chemo/surgery/etc side effects.
In your situation (since you sought advice....) be careful if you catch yourself reading suggestions and finding lists of reasons why they won't work. Don't undermine your energy. If someone else's idea doesn't work, just nod and move on. Find something that does. You, and Amy are in a rotten situation, and I'm not suggesting downplaying it. It sounds like you really love her, and that is a huge source of possibilities. The rules have changed though.
PM me if I can be of any use.