Hi Kiki and welcome!
I can fully understand your feelings. I'm wondering from a few little clues whether you may be on the autism spectrum. It would account for all you say. If you are, and you're female, misdiagnosis and underdiagnosis is only too common. We are not understood.
Is the stress at uni caused by the social aspects of being there, work overload or both? Why do you think your brother is so cruel to you? It hurts me just to read about it. Your mum shouldn't allow him to be like that!
I think my parents also got frustrated with my MH conditions at times, but they never knew I had autism and couldn't help being the way I was (OCD commonly comes with it, and I have that too). I was only diagnosed as a result of being unable to cope after losing my mum. You're not
emotionally blackmailing your mum, and it's a cruel thing for her to say to you. She should be helping you find the help you need, and supporting you in your difficulties. Talking like that is only likely to make you more depressed, and it further encourages your brother to be mean to you as well. I'd be low and tearful too, given what you have to endure. I've been like that too many times in my life - and all because others misunderstand me and behave cruelly.
I'll help you as much as I can. Please don't hurt yourself. I come here at least twice every day, so you're not all on your own. x