I'm depressed and I wish I could relive my childhood again?

I'm fifteen. I smoke, sometimes drink, and I grew up in a wrong way. I watched Toy Story today and cried my eyes out, because I remember always watching that when I was little. I looked at some of my old toys and Beanie Babies this week and cried all day. I've lost a lot of my childhood friends and family friends, and we've all literally gone our separate ways. One is a pothead and a loser, one drinks and works her *** off, one moved to Tennessee, one got a girl pregnant and after that I haven't seen him since, and one I see sometimes but now I can't because his stepdad took his car away. I still haven't moved on. I'm a very emotional person and I have trouble separating reality from fantasy. But just knowing the fact I can't go back in time and relive the memories and change myself and be a carefree little kid again makes me feel completely useless and depressed. PLEASE HELP ME, I'm crying just tapping the letters of this on my iPod.