I can relate to the secure feeling that drugs provided. I felt more comfortable knowing I had weed on me and beer in the fridge and was even more satisfied knowing I was able to get something to put in a spike for that day/night/whatever.
I hate to sound like 'old head' here but, you are young so your mind/body is still going through a lot of natural changes on top of the changes you are going through in lifestyle so shits going to be a roller coaster for a bit. Everyone has to endure that but you got the 'addict' thing happening as well which makes it a bit more challenging.
The MMA thing might be a REAL positive. Folks like us tend to go hardcore into the things we love. Shit, you may become the next Royce Gracie (yeah, I'm showing my age

). For me, I started exercising pretty heavily and that helped with my moods and general confidence level. Maybe you can bump your workouts/training to the next level? Or, perhaps since you got the exercising of the body covered, maybe balance that with stepping up in the area of school and exercise the mind more?
Dude, I tend to be a bit aggressive and I apologize. I don't mean any harm and forget sometimes that my solutions may work for me but that doesn't mean they'll work for others.
I'm just throwing shit out there without knowing too much about ya. Thats why I think its best to shoot the shit with your support system. people who see you regularly and
know you. I wish we could take your depression away but that's something that is going to have to be your personal battle.
Please just stay the course and give this being clean thing an honest effort. Its going to get easier. It won't happen right away but it
will happen. For me, the best reward I received from getting clean was finally being comfortable in my own skin. That was HUGE!