A very important thing that I learned from being bipolar is that sometimes I will view life with a beaten down cynicism and futility. This often means that everything, regardless of its difficulty or significance to my daily life, seems terrible and often scary. It took a lot of time before I was able to recognize that as something out of my control, instead of me being whiny and lazy. Job interviews scared the shit out of me. When I was at my worst I would hunker down and not deal with it, instead just contemplate suicide and think about how futile life was, as if it was some sort of therapeutic mantra in a time of need.

When I was a teenager these thoughts would often spiral and culminate in a very cynical and stereotypical view of my future and the rest of my life in society. So even if that seems "angsty" to an adult, I can still relate to feeling the same way at your age. But your dissection of life in modern society is wrong, and it's important to remind yourself of that.

I will admit that I can not relate to ever being as emotionally invested in a relationship as you are in my teens. If I had to guess, I'd say it was because you're a little asocial and she's sort of been your primary friend, and if you lose her you feel like you risk a huge upheaval of your social routine during the last few years, which is scary.

But please try to remember this. Saying "I have no real interests besides x and x (often gaming)" is one of the most common thing that teenagers these days say. I've seen 100's of posts with this line of thinking on r/depression and r/suicidewatch, and I can very much personally relate to it. So don't worry too much about that yet. Believe it or not, the majority of people who choose a path in life do it because they're taking a risk with the option of jumping ship if they hate it.

I would definitely go back to therapy if I were you. It sounds like you are in need of exposure therapy, which is a way to battle social anxiety and compulsive negative thoughts. In the start my therapist would just let me talk and help me work out the stuff I was dealing with, dissect it and basically show me that it was illogical. Then after a few months I'd move on to exposure therapy.

To tldr that last bit: you need a change in your routine. You're unhappy, you're dealing with negative thoughts and you're having trouble with social scenarios. A girlfriend wouldn't solve these problems any more than not changing anything would. Try to go outside more, try to force yourself to forget about her, try to reconnect with an old friend, you choose. Your biggest enemy right now is not changing anything about your daily routine.