Dude, believe it or not, many if not most of us drug users have been there or close to such a situation in life. Abusing drugs, isolating yourself, losing friends,...Addiction is a b*tch, we all start losing friends once we start isolating ourselfs. Dont be so obsessed with it like this is one huge dramatic situation that is only happening to you with nowhere to go. Its really not.
Perhaps you are alone now. Its not permanent. Friends come and go, some stay. You know that life never stays still, you change friends as you change yourself, your life, as you mature, relationships change, you meet new people, new girlfriends, and most of all new opportunities. Try not so much to stick to your idea how everything should be like. You cannot control it. Right now, its probabily best if you deal with your addiction to opiates. At least minimize it as much as possible or if you have to go on suboxone/subutex or morph. sulphate ER... And dont worry that you fried you brain or anything like that. Its not true. It is just an excuse. I have this friend who constantly tells me because of his use of cocain he also "fried his brain". He constantly uses it as an excuse. ITs not true. Ive also done coke for years, also LSD and whatnot, it doesnt happen like that. Youd have to be a crazy extreme user.
Try not to obsess yourself so much with what you should be by now or where you should be. Dont compare yourself so much to other people. Its sad actually how this culture and society dictates your life and where you should be when youre 20, 25, 30, even if its not for you or youre not ready. It might even be a blessing for you. Yea sure, other schoolmates might have business and children and whatnot but that was not really your path. Its nothing bad. Most people who get married and have children when its EXPECTED of them or when they think its right it is mostly a sour sweet thing. Most people today are not mature enough until later in life.
And business-wise, you seem to be an intelligent guy, I dont think you will have that much problem getting back into employement and possible success when you are ready to return.
So please, stop thinking so much in fixed terms as if this is it, its how it is and it will not change. Everyday you wake up you are making your future. Its not written anywhere. Sure, have goals, have plans and ideas but DO NOT cling to them will all your might. Things are not certain. You can change everything if you wish. Start with your addiction because it is dragging you down. Being alone, feeling inadequate career-wise, girlfriends, its all in your reach. Just dont obsess so much about what has been or where you are now. IT is not important. And the moment you think about it, how youre alone, the moment is gone. And the chance to change it was in that moment. And it will there in the next one to.
Good luck man