Gidday Daniel - thanks a heap for having the courage to reach out.
I see that TonyWK and Petal22 have already given you some great advice.
I have a friend who went right off the rails at a similar age to you and is now back to full function (almost) - let me share his/our successful journey with you.
So he was into heavy drugs and alcohol for over ten years. Then formed a relationship with a very unstable woman. Things got heavy and ultimately, the police got involved.
That's about the time when we met - I had been on a bike ride with others, we were having coffee at a cafe and I asked him to join us in the coffee queue.
We all got chatting and he became very interested in why we ride bikes and how we feel. I think our animated conversation and bad jokes was like a tonic to him. He was open about his ongoing Alcoholics Anonymous meetings and heavy drug background. After meeting our group a few more times at the cafe he ended up buying a bike and joined us. Even though we positively egged him on, we were still amazed he did that.
Initially he was very unfit but stuck with it and I coached him a lot with chats, rides and texts. Three years later he is beating most of us in races and says he had never felt better, or had more self esteem. He had a couple of relapses and mood swings or course, luckily they didn't last long as we told him we missed him, but credits our group and the bike riding with his recovery. He recently put an open post on Facebook of a photo of himself on the bike (now on his third bike but the way, cost $4500!)
Here's the point - of course I cant judge your own situation Daniel and wouldn't want to, but the above true life story happened because he needed the company of upbeat positive mates, and the endorphins from exercise are amazing for feeling great and lifting self esteem.
I would have struggled to believe his transformation it if I hadn't been part of it myself.
So I would encourage you to try joining some sort of activity group - preferably physical activity. Be open with them and they are bound to support you. The hardest part will be the first step and making the approach. Make sure it's a group at a social level to welcome newbies - some bike clubs or others might be a bit snobby.
From experience, MeetUp is a good social activity group.
Out of this create some personal goals, build on them and away you will go. Hooked!
Hope this raving has helped a little bit and all the very best to you.
Keep me posted!
Regards, The Bro