I'd like to welcome you here and also say I'm glad you have already met Sophie_M, who gives excellent advice - I particularly agree about the Kids Help Line
I did notice one thing about your post, you said "hidden away from the world, both terrified to join it yet desperate to be part of it. "
Really speaking that is both understandable due to the bullying - which leaves deep scars you may not even realize - and also good.
Yes I did say good. Good because you want to be part of the world, which is healthy and hopeful. You most certainly deserve to be part of it -and have a good life (even if you find that hard to believe at the moment.)
Good also becuse it is fear holding you back. Fear can be useful , if a sabre tooth tiger comes in your cave you head for the hills. It can also be a right nuisance -a rabbit frozen in headlights before the driver dips the lights and it hops away.
However fear can be overcome. No, not easy, partly becuse you don't know what to do, and partly becuse it may be too big a job for just one person. Still overcoming fear is why there were saber tooth hearth rugs.
I've felt it, it made me hide depression, anxiety and suicidality for a long time. Eventually I sought medical help and am now a different person.
So may I suggest your first step towards a fuller happier life is to go to a GP, and in an extended consultation explain how your life has been -then see what happens.It may well lead to treatment, as it did for me.
If the idea of a face to face talk is too much do what many do and write it all down first -then share the paper. It's a good way of doing things as you have plenty of time to get things set down right and the doctor has a complete list to work form.
Which reminds me, please do not make my mistake and leave things out. If you have been thinking of taking your life just say so, nothing terrible will happen. I left things too long and was harder to treat as a result.
I'd like to talk with you some more, in the meantime please think of the things in life you enjoy, make a list. Anything, from cake to racing cars, musical groups to reading books, whatever, no matter how small or big.
I look forward to hearing from you again