It's very sad you had to witness your mother's illness, you and her suffered a lot but she's resting now, do you think there's a reason why you should keep suffering?.
Your mom maybe fought all those years because she wanted to live, I just lot my aunt to cancer 3 months ago and even after all doctors told her she had days to live she wanted to get better, that must tell us something about how precious life is and why we should try to make the best out of it while we have it.
You mentioned you just started singing again, that sounds like a very good thing, you must do things you enjoy that help you become a better person, not things that might make you feel okay but will destroy you because death is present anyway, we're all going to die at one point or another but there's no death for as long as there is life, you're here for a reason, to be happy.
I don't know why some people have to go through the most difficult experiences during the first years of their lives (like you) but whatever it is there's no reason to make it last longer than it should, you're not going to forget what happened but you can find a better way to remember it.
I lost my father when I was around your age, people often said to me "You'll learn to live with it" and to be honest I never did, I accepted he was gone but there has never been an "I'm fine with it" mentality, I can think it was the best for him but that's about it, and if you ever reach acceptance that's fine and if you ever feel there was a reason for things to have happened that way it's fine too, just get to a place that feels right for you.
Don't give up.