I hope this is okay to post here. But I need advice on. How to let go of my mom.

I just turned 19 and I had my first baby 7 months ago, my mom has been out of my life since I was 15, she deals with alcoholism, she's always has ever since she was a teenager. My parents divorced shortly I turned 16 my dad got full custody of me and my brother after we got into a car accident because she was drinking, we never really saw her much after that, she has popped in from time to time when she is "sober" she never stays sober for more than a month tho.

2019 was a really hard year for me, my little brother passed away 5 months ago and my BF just passed away almost 2 months ago and I've just really been missing my mom and I get so angry and upset that she isn't here, the times I needed her the most she was off drinking and seeing random guys and my dad works all the time and he's also going through a lot, he really struggled with the divorce but he has moved on and has a new GF and I love her she's great but I want my mom back. I know shes a toxic person and she isn't a safe person anymore, idk how to let go tho, like why couldn't she choose us, her kids instead of alcohol? I also can't help but think my brother would still be here if my mom never left.