My experience got worse before anything got better, but depending on where you're at, it might be helpful to you so I'll share it anyway.

My dad was diagnosed with stage four prostate cancer shortly after I got out of the military. I was already dealing with a litany of issues related to post-separation and military service. My first piece of advice is to decide what level of proximity you can maintain with your mother without letting it affect you. I saw myself in my dad, especially in his lowest days. Make no mistake, my dad has (spoiler alert: and continues to) fight cancer valiantly, but in those early days there was a lot of regret that he even chose to live. On the other hand, my dad being able to confide things in me was immeasurably good for him, and something that therapy and a stranger would likely never accomplish. These days I call him once a week and we talk about things he's up to, I listen to his day, and help him make decisions. I try to encourage him to get out, share his story, and make friends -- his life seems to improve as his circle expands. When I was caring for him day to day it took its toll, but there also weren't many other options. In life you sometimes have to walk with someone through the shadows of their valleys, helping them build the tools to hike out of the valley.

When you determine your safe distance, it's easier to plan things like learning back into your life. My dad loved hearing about what I learned and loved being shown what I was up to. Doing this kind of stuff inadvertently helped pull me out of my own drinking spell. Watching me grow as a man, and heal in my own way seemed to help him all the more. At the very least, it took his mind off of the idea that he was stringing his life along a little at a time with various treatments.

In times of stress it's often easy to fall into routines. For some people those routines are working (and overworking) or drinking (and over-drinking). I managed to accomplish both at the same time. I only managed to undo these routines by keeping a journal and reading my thoughts a day later. It helped me reflect and deal with my feelings in a detached way. I wrote several times that I knew what I was watching: my dad was dying and I had a choice to make in how to deal with that. I didn't know what choice I would make, or even if I would be cognizant of making said choice. How you deal with that reality is entirely up to you, and there is no wrong decision except self-destructing. The important piece that I would leave you with is have a way to audit your thoughts, because inevitably that is what helped me the most.

The last thing I'll say is a continuation of my last point. Eventually I realized that my dad will die, and some day all I will have is voicemails and letters or things he's left me. My memories of him will continue on, though. The good ones, the bad ones, and everything in between. When I go home I try to make good memories with him. When I was a kid we bonded by playing video games. He can't play them as good as he did back then, but I'll bring an extra controller and we'll play together. These memories are the ones I hope to have with me after he's gone, but in the moment I always aim to be present.

I don't know if any of this helps but these are the tools I used to build a career and (try) to stay sane during that time. Things do get easier with time of course.