This must be so hard especially when you’re so young and having to deal with this alone.
You could anonymously call the RSPCA or dogs trust to rescue the dog as it’s clearly not safe there.
I’m an adult and I don’t know how to deal with my partner so how can I advise you what to do. I’m assuming they get drunk and then can’t remember how they acted and then make you feel like you’re causing a fuss over nothing?
Do you have any ‘safe’ relatives you can confide in?