Dude, you're 20. Go back to school and get a freaking diploma. Take those 4 years to figure out what the hell you want with your life. After that you will be.. what... 24? Life haven't even started yet kid.
Diploma in what? I'm all over the place, and I can't just choose one area of study. What if I want to study art but the diploma will be useless? What if I want to study business but end up writing TPS reports for 100 hours a week at Wall Street? What if I want to study math but will end up hating whatever it is I studied. The possibilities frighten me and excite me at the same time.
1. Don't get paralysis.
2. Pick something that gives you good career options. The rest are your hobbies (and it's good to have hobbies).
4. Be cautious taking on any educational debt -- make sure it's worth it.
Your career will take many turns but you want your opening move to be strong.
Frankly, if you can program and enjoy math, your future is bright. When you love your work, you won't need the escapism of substances.