I hope what I write helps.
At no point did I say that you were toxic, but yes, I did find so much of your post to express a toxicity that was palpable by just reading it. Maybe there are other, better words? Unhealthy, maybe... but toxic still seems pretty appropriate, even if you find it to be overused these days.
So, to clarify, my intent was to say that your brother is not to blame for how despondent you appear to be, nor is your mother (not matter how damaging she might have been)... I will also say that nor are you (without denying personal responsibility), because the whole concept of blame is what allows the toxicity to maintain such a presence in your life. That has to be dropped as soon as possible, for your health. You are obviously an adult, and so the onus (and the freedom) to claim ownership of who you are, what you are, and how you are is upon you alone. Look at your own actions: you seem genuinely angry that your brother apparently only considers you as a source of income, and yet it is you who started it off by furtively buying substances from him.
Most of us on this board have been through significant abuse, as well, so I don't feel guilty for telling someone who is very clearly in a great deal of pain that it only harms you more to hold onto it. No matter how much it hurts, a shoulder to cry on is not what you need now (in my opinion, and that's what you asked for with your original post). If you want to feel better, it will take ongoing work, and perhaps different work than what you've already done.
If I didn't care, I wouldn't have written anything in the first place. You are obviously suffering and I sincerely hope that you can start to feel better. When I consider my ongoing recovery, I can thank folks here on this board, in my groups, and in other aspects of my life for their honest appraisals of my situation.