Hey there, all I can say is wow you have been through so much for 18. And it sounds like you have a lot of hard situations in your life. I will say this--I was 25 (fairly young) when I stopped drinking in AA. I started drinking at 18 and became an alcoholic very quick for some of the same reasons as you--shyness, felt more outgoing, more happy. I got to AA at 25 and I have stayed sober from alcohol for almost ten years. My life got SO much better. I met my husband, got married, things were great.
Unfortunately, this year I fell back into the trap and fell in love with pain pills. They did just what alcohol did for me without the hangover. But their "magic" wears off quite quickly and now I am an addict too. I am tapering off the pain pills for the second time this year so my withdrawal is no too severe.
The suicdal thoughts--I have had them over and over. I know them well and you feel hopeless that things will ever be better so why not just end it. I can tell you from experience things do get better if you just have a little courage to try something different (an AA meeting or something like that). I finally feel like I am coming back to myself after being depressed and suicidal for months. I have family stuff too--divorced parents, brother who won't speak to me (he is a marijuana addict),but I can say I do wish I was with my mom tonight. I am with my husband though for Christmas and for this year since I was so recently suicidal I didn't travel. They live far away.
Anyway, all I am saying is suicide is final. I know you feel hopeless I have been there but it does and can get much much better. I actually think the pain pills turned on me and made me feel worse at some point. But I am glad I didn't kill myself a lot of people would miss me and I am sure many would miss you.
Hang in there, I am praying for you. Merry Christmas.