What you are going through is a FEELING of despair and uselessness. Feelings are temporary. You know I'm right because there are times when you FEEL great. Think about what precipitated those feelings.... chances are, it was when you felt important and needed.
This is why people often advise those who feel like you do, to volunteer their help with a group. It's a way you can begin to feel needed and important again.
If this kind of thinking gets you further and further into despair, reach out to a counselor and get to talking..The other things written here were pretty good too.Good luck!
life is what you make of it. there will always be hard times, but you can get thru anything with time and friends. keep your chin up and keep moving forward .