@MMAN might be time to think about all this a bit differently so you don't feel sad. Treatment is so great these days and survival rates are just amazing.
Maybe get some support through a counsellor. It's alot to process and some people are ok about it all and some people need a bit if help to get through it. It's great to talk here as we all understand but you have to reach out to some professionals if you are struggling too much.
Try to go for walks, be busy with a little project just for you, for example treat yourself to lots of moisturiser and spend time caring for yourself. Just do so things you like and turn this around to focusing on getting better. You will get better.
Start with something small and build on that every day. Gratitude is another thing which really helps. Try writing down 3 things you are grateful for. Could be as simple as I am grateful for my morning coffee.
Wishing you all the best in your treatment and recovery. ❤💐