We are all here for a reason and just knowing that your mom COULD have aborted you if she had wanted to says you were meant to be here....you have a purpose....

It sounds to me almost like you feel as if you are the odd one out of the family....but I am sure your family loves you and wouldn't want you to feel that way.
Where is your father? is he in your life?if not could it be that you are lonely for him?

I hope you find your way out of this depression soon hun.. and please.. do call a crisis line if you feel suicidal again... it isn't the answer...

Peace, Faith