It is that easy. Stop making excuses and start making better choices. No one can do it for you, and while I'm sure you have trauma, your traumas don't dictate your choices unless you let them.

You’re going to ruin your life and all your relationships if you keep making excuses for your shitty behavior.

I’ve dealt with depression for the past 11 years of my life

You need to talk out everything with a therapist. And what you say to a therapist is not going to get back to your friends. Try to get your family to get you an appointment with a therapist. Or do it on your own if you can. It sounds like you have had a rough childhood.

Young people who have been abused and mistreated/ not loved properly have tendencies to use substances. You are on a dangerous slippery slope. Weed is one thing (it’s not great for kids as it affects the growth of your brain as you get older, and it can cause mood issues). Try not to mess with it until you are older. But at least it won’t kill you. Alcohol and pills are another story, they will lead to misery. I’ve just had a cousin die from alcoholism in their mid 30s. Another cousin died from a drug overdose, either fentanyl or heroin. Right now it’s taking pills “because it’s fun”, on s year or two it’s becoming addicted to heroin. And if you think the urges are hard now you have no idea when that addiction comes.

And even before a heroin / opiate addiction comes you take a risk each time you buy pills from on the street as they could be fentanyl. The amount of teens dying from overdoses the past couple years has skyrocketed.
You never know what you are really taking nowadays.
Get into therapy, hopefully you find a good therapist; open up to them. They will help you talk out stuff. It can work wonders to get feedback like that, to trust someone with your thoughts. Someone who cares about your well-being.
The friends that pressure you / or are a bad influence on using alcohol & pills are not good friends. Real friends look out after one another. Get close to friends who don’t use that hard stuff. And screw anyone who’s associated with gangs. Even if you open up to a school counselor you don’t have to talk about anyone else. You are not snitching. Going for help for yourself is about you, not them.
I hope you can find a better path for yourself because right now your future doesn’t look very good for you. Please try your absolute best to get help. I hope you do, and that you will find peace within yourself to where you don’t need any of those dangerous hard drugs/ alcohol. You need a trustworthy confident to lean on and to talk everything out, and real friends who actually look out after you.

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.