You don’t have to tell them about people involved. Just about yourself and what you are going to. For all anyone knows you could be hanging out with other group of people as well.

I also used to abuse alcohol in my teen years. The only reason I stopped is because I lost all of my friends which was a blessing in disguise - yes that was the darkest moment of my life but I got through that. Alcohol doesn’t help anything, it just causes more problems - even now at 24 I drink on weekends but I know I should cut it off as it doesn’t even bring me that much fun as it used to.

How to change things - start by not looking for excuses and reasons not to but by finding solutions. Like “I have substance abuse problems- let’s start by lowering the intake. Instead of doing that I’m gonna go on a walk, or do a hobby (for me super helpful was teaching myself how to play the guitar)”. Start small. Also I’d advise cutting the friends off. Trying to join after school activities to find friends with likeminded interests.

As for self harming - I used to do that to try and replace emotional pain with physical (having emotion dysregulation/hyperemotionality didn’t help but I only learned I have that a year ago). What helped me was finding a meaningful person to me who I didn’t want to let down so I stopped it for most part. I’ve attempted unaliving myself. Ended up spending a month in mental institution. Couple months later tried to do that with antidepressants had the worst time - so bad I decided to stop using them in general. You know what I discovered? That even if I felt good I wanted to make myself feel bad. That I had this self sabotaging tendency. So I’ve stopped that. You have to learn to love yourself. Start by looking in the mirror and telling yourself compliments and how amazing you are. Even if you don’t believe it. You’ll say it until one day you’ll be like “you know what? I do like me. I’m amazing. Fuck the world - I’ll be the best version of myself for myself”. You got this.

Sorry for the wall of text but I hope that you read it and hopefully this will somehow help. I hated when people told me this but - you’re still young and have years to live. It does get better. You and only you can make it better. Believe in yourself.