People don't stop talking to you for no reason.
You say you've started drinking, smoking, doing drugs and sleeping around. All of this affects your behavior. And it likely affects how you interact with your friends in a negative manner. Its not that they quit for no reason, but more likely you have driven them off with the changes in your life, and the way those changes are affecting you and how you act and treat your friends.
Right now there is a choice to be made. Continue this cycle of guilt/negative feelings, which makes you act out, which causes guilt/negative feelings, which causes you to act out more. And continue to see it and do nothing to change it. Or you can realize how badly you're ruining yourself, your body, your mind, your spiritual walk, your relationships, your self worth and your life, then do something to change. Because all these things you're turning to to make yourself 'feel better' or 'forget' only create a bigger need to feel better or forget. So you are only making things worse each time you continue these patterns.
Quite simply, quit. I know some things are harder to quit, and some of these behaviors may take time to quit completely, but the longer you sit here sulking and wallowing in self pity, the longer it's going to take to get your life on track.
Maybe call up your old friends and ask them why they left. And be ready that you may have to hear some things that are hard to hear, but be ready to own up to them and deal.
Or move forward in your life and find new, good friends that won't encourage your behavior.
There may have been some things that started causing you to feel bad that you couldn't control, but How you have chosen to handle those feelings is on you. Right now you're the one causing the pain in your own life. And you're the one that continues to make the choices that will keep causing you pain, or to make choices to stop. You can't blame anyone but yourself. And i say that not to put you down, but to point out that you can't blame anyone, or any circumstance for where you're at. Even if bad things happened, it still falls on your shoulders because there are better ways of handling problems without resorting to the things you have. And since you made these choices to start, now make the choice to stop.
Perhaps the real need here is that you need to stop trying to handle things on your own and find someone to talk to, that will listen and help. And who is knowledgeable, not some clueless friend who will only make things worse.
The worst attitude in the world is 'i don't need anyone else'. Especially when it comes to going through hard times. Rather than running to men who just want to use you, run to someone you can trust and tell them what's going on.
It's time to stop hiding from your problems and to grow up and little and start dealing with your problems head on. Sober. This is the only way to regain that happiness that you once had.
If you have no one to talk to, i'd be happy to help. Or you could hang around the forums and find an older woman that could talk with you. But one way or another, you need someone to give you some guidance and support in this rough time. Don't think you can do it alone.