I'm so sorry you're having a bad time, Elf. *many, many hugs* Keep hanging on and remember that things will get better (I know it sounds cliched, but my own home life is seven kinds of stormed up right now, and that's what I keep telling myself.)
And you are not being selfish in any way. From what you said, you are definitely in a stressful situation, and it's completely okay and normal to feel sad, angry, or depressed. Remember that I'm always there if you want to talk.
*more hugs*