I've read everything you have posted. You say you have tried doctors. Did they give you a diagnosis? Like depression perhaps? One thing about that is there would by an Rx that actually might alter the chemistry of your brain and lift up your mental state so that you can see things differently. The hard part of that is finding the right one for you, but this is a place to start.

Also, taking those baby steps of making yourself get out everyday, not just for cigarettes, but somewhere that there are people. Even the park, or library to find something different to read. Or a book shop. No, it won't do everything you want, but it will get you in the habit of getting out and out of your comfort zone. It is important to do this.

You seem to have turned so inward on yourself that you are having trouble getting out. It would be a worthwhile effort for you to find an interest outside the house. People meet when they share something in common. You may not think you have any interests, but by looking at something like, MeetUps.com you will see there are all sorts of things people do, just because they want to share an interest they have with someone else. It's a place to explore what others find interesting too. Even bike riding is in there, along with many other things,(cooking, Legos, languages, movie watching) so see what is going on outside your four walls.

The world won't come to you, you do have to make a little more of an effort if you want to find friends and especially a girlfriend.
Girls like guys who have interests to show them, even a movie or gamer collection.
You are young and still have a whole life ahead of you. That may sound hollow to you now, but you can turn this around. It is up to you. So make the call. Ask for help if you need to. Don't give up because you've tried before. You just didn't find the right thing.
I'd start with finding a doctor who can treat what sounds like depression first. This will be huge if you can get a handle on it. It may change your life.

I wish you only the very best as you explore ways to get the life you want. Keep me posted, I'd love to hear...