You seem to be implying that depressed people are selfish, which is generally unhelpful, false, and disrespectful to those who have suffered.
Really don't know much about clinical depression, but heartbreak and mild depression that average people go through can I've found to be lessened by helping others. Probably mainly because it takes your mind off of the fact, and also because you feel fulfilled in the end. Two things that don't happen if you sit at home sulking alone and constantly replaying your past over and over.