Simple Question

My brother apparently has horrible depression; most of the people I get close to have depression, too. I know it’s generally a psychological thing, and I don’t even know that many people to be sure, but I can’t help but wonder. I’m not good with emotions, and I’m very introverted, so I’m not the best at knowing how to comfort people or spending enough time with them. My brother gets worse by the day, and my friends never get better. Am I doing something wrong? Is it me? If they can’t take care of themselves, and I’m not supposed to (irregardless of whether I’m good or bad at it), who should?