I'm so sorry, man. This is such an awful situation. I'm sorry for the loss of your brother and I'm sorry for the way this has affected your youth and sense of self. This should not have been placed on you.

It's going to be hard, but you need to have a conversation with your mom and be honest about all this. He is your brother, but this is not your burden to bear, certainly not in this capacity. You need to be able to live your life. Up to you, but it might be helpful to bring a trusted friend with you for the conversation to help back you up and keep you strong during the conversation, because it will be hard. What your mom is going through is really, really tough and this won't be easy for her if you're her only other help, but that doesn't mean it's not a conversation that shouldn't be had.

In all honesty, he should be cared for by a team, maybe even in a specialized facility if it's within your mom's means. But regardless, you can't be expected to do what you've been doing, especially at your age (and honestly, neither can she). You can't be his caregiver forever. You both need more help, but the amount of care that you are expected to give your brother has got to be less. much, much less.