Well. I don't have any wisdom, but I am here to tell you you're not alone.
Strangely enough, I'm also turning 21 next month and was diagnosed with depression and anxiety 5 years ago. The end of the year is always tough, because (at least for me), it's always full of a lot of reflection. Another year has passed? What happened this year? Why do I feel like I'm worse off than when it started? Am I making progress? Is life always going to be this way?
I don't know about the betrayal piece, but I certainly hope you can find some peace.
And if you need someone to talk to, the door is open.