Do you think, perhaps, you are taking on more responsibility for other peoples actions and feelings then you should be? We are each responsibile for our own feelings. I know you don't want to see your brother make a mistake but you also should not have to act as his counselor as you have your own issues. I would suggest you point him in the direction of his physician and a mental health counselor.
I think, it's helpful to tell yourself, "that people do get through depression and thoughts of self harm ." It's also helpful to know that help and treatment for depression exist. The difficulty, sometimes, is knowing where and how to get it.
Here are some numbers you can provide to your brother :
The US Suicide Hotline 1-800-784-2433
NDMDA Depression Hotline | Support Group. 800-826-3632
Suicide Prevention Services Crisis Hotline 800-784-2433
Suicide Prevention Services Depression Hotline 630-482-9696
As far as your job, if you prefer to continue working with what makes you comfortable, speak up and tell the truth. Avoid the anxiety by taking on what your just not ready for.
Remember many people in school become confused along the way wondering if they are going down the right path. Look at your options. You do have control and give yourself permission to change your mind. The one thing you have the most control over is your own feelings. If you need help for you, put yourself first and seek out your own therapist to help you through this tough time.
Blessings to you