It seems like you are lonely, you need to find some goal in life, like aim to achieve something and keep yourself busy so you don't have time to think these bad thoughts. One thing that works for most people is working out and improving your health and body, which in turn helps you feel good about yourself and you would want to go out and make new friends have fun and enjoy life. OR learn something new that you always wanted to but never got to it.
What you need to do is stop feeling sorry for yourself and think of all the less fortunate people then you.
If you don't have any close friends with whom you can share all that you are going through then it may help you to start an anonymous blog and pour your heart out over there.

If nothing helps then go to a Psychiatrist