I'm so sorry that this is happening to you, it must be rough to go through this. Although you can' t control them having a divorce, or him having a addiction, or other things that come with your parents divorce,you can try to tell your mom how you feel about the divorce, even though you know you can' t stop it, it would still be good to tell your mom your feelings about this so that maybe there might be a chance for slight changes. like how you feel mad or sad or another feeling and how you know you can' t change it, but still can' t help feeling this way.
For your mom, ask if maybe see if you guys can stay over at a relatives house that you trust, if it gets to that. or check on your mom every once in a while to see if shes okay if that helps you.
Addictions are really hard to get over,and it hurts a lot to see someone you love struggle with this, sicking in the heart sometimes, but try to see if you can help with your dad's addiction in some way. Most likely, you will not, but try searching up how to support family members with addictions on the internet, or youtube. you can' t tell someone to stop having an addiction, since their body mostly comes adopted to it and it becomes the normal, which its hard to come out of a habit if its the normal for you and your body craves it. so it might take a long time, but if you find some good information tell your mom about it, since she will probably want to help your dad come over it even if she is divorcing him.
I hope this helps your whole situation get better, and it's terrible that you have to go through it. i went through something similar, Except my dad died so we never got to resolve it, and no one ever told me what was wrong and why we could not see my dad,( i was somewhere between 7-8)
I'll pray for you and your family, and also for your dad's addiction. it will get better, it's just going to take some time, and a lot of work. hope it gets better