I'm so sorry OP!
My sibling was diagnosed with secondary cancer in their early 30's. Chemo doesn't necessarily mean debilitating IV chemo, my sibling has a pill form, their hair hasn't fallen out and they still work full-time whilst being a parent to young children too.
When they first got their diagnosis my world fell apart. Now in my life there's the "before their diagnosis" period and life "since their diagnosis" period. At the time I just thought of their diagnosis as a death sentence. But you truly do have to treat each day as it comes.
My sibling has had good consultations following regular scans and also had some slightly not good news at some consultations. You might have peaks and troughs.
As others have said this really isn't a death sentence nowadays. Advances in medicine is changing all the time and I am so so grateful to still have my sibling.
I haven't read the whole post as some stuff is still triggering for me so I have to be ignorant to protect myself so I'm not sure who if anybody you have told. But do confide in somebody, for mental support. There are great charities out there as well as websites that specialise in products that can comfort and help you during treatment (particularly chemo).
My sibling is living their life to the absolute best they can - even more than they did before the diagnosis. As cruel as it sounds It can sometimes be a blessing. You really do have to find the small blessings with this horrible and cruel disease.
I hope none of my post is upsetting to you. Sometimes people wish well but will use terminology that can actually evoke upset, which happened to me in the past. I truly wish you the best xxx