Am I needed?

Sometimes, I feel like I'm not needed... I've cried all my hearts, figuring what my purpose of living in this world is... Eventhough I know that I shouldn't doubt God's gift, it's just on my head... I have many friends, but I don't know if they really care for me and love me... I know what I'm doing right now is wrong, doubting my friends is just a big mistake... But, I need answers in my life... Could somebody help me figure it out? I'm having mental problems right now...