Thank you for writing. I think you already know that the one incident with your mom didn’t “shatter” your relationship with her. You already know that she isn’t completely stable. After all, she stayed in an argument with you for hours. She has a history of self-harm. She was so unable to cope with your problems that she absented herself. That doesn’t mean that she doesn’t love you. It only means that she has all she can do to manage herself. She can’t manage someone as close to her as her own daughter needing her help. The problems of others ultimately don’t affect her. Yours do.
Adding to the issue in your case is that you’ve been “parentified”. Your family has come to expect you to be the strong one. It probably terrifies them on some level when you also have needs and then, maybe, can’t be there for them when they need it.
As for your twin and your friends: Please don’t interpret their lack of response as lack of caring. Often people withdraw or joke when they just don’t know what to do or what to say. They worry they will say the wrong thing or make things worse. So they avoid the issues, change the subject, or drop out of sight.
You do need support. You do need a place to express all of your feelings without fear of judgment or rejection. It would be great if such people could just appear now that you need it most but that’s unlikely. It will take time to make friends who see you as an equal, not the always strong one, and who can reciprocate your warmth and care. They are out there but you probably need to be in a better space to find them.
So — I do think you should see a mental health counselor. You are anxious, depressed and lonely. That’s plenty of reason to seek out the ongoing support and practical help a counselor can provide. You need it. You deserve it. If you don’t know how to find a therapist, talk to your school counselor or your doctor.
I wish you well.