I think you have to try and be empathetic towards your brother. Clearly he's had lots of thoughts tightly wound up in his head which puts a great deal of stress and anxiety on a person. You have to understand that it's not your fault. You didn't all or any of his problems. It's long past that stage now, you should be there and help him, not get caught up with what happened in the past. You also have to know that letting it all out is his method of coping with it, so if he gets annoyed or angry with you then don't read into it. He's just letting it loose and sad as it is, you're just there to assist in that. So think of it as you helping him cope if he lets it out at you.

You are his brother so you should support him all you can. Make sure he's okay, if you see that he's looking sad or down talk to him. Ask him what's up and try to make him happier. Go watch a movie together or make jokes to raise his self-esteem and his mood. If he finds out that you're cutting he's only going to think that he's responsible for it, and that will only make him feel even worse. You obviously don't want that, so trying to stop cutting altogether is a great idea. It's definitely not easy but it will make you feel better and will prevent anything like this from happening.

As another member suggested, you might want to look at going to a counselor. Either you and your brother separately, or together. I think being together is perhaps the best option because you can give feedback to each other and let out all your feelings. Seeing you two respond to each other is beneficial to you two as well as the counselor. They will be able to assist with coping with this and suggest methods to help resolve the problem. There is only so much either of you can do alone, having a 3rd party there independent to the situation provides a fresh look on the situation and they can often pose ideas or thoughts that you wouldn't normally think about.

Just look out for your brother. Talk to him, but don't approach him all the time because he might get the feeling that you're nagging him or making him feel like a baby. Remember, the future is bright, he's over the worst part now, so be there and support him. But equally make sure that you are alright yourself. Don't blame yourself for this, and don't overlook it. Go have fun with your friends as well, make sure that both of you are happy and enjoy your lives. Doing fun things helps to relax you and take your mind off of everything else.

I wish you the best of luck, and if you ever need to talk, feel free to PM me.

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and victorious in war shall be made glorious in peace.