I'm depressed again
Why are you feeling depressed again?
Whenever I'm high on life, death is looming.
Almost everyone has a long life still ahead of them, so you shouldn't worry about it ending.  If depression continues to haunt you, though, you should talk to your friends and family, and maybe to a professional.  There are programs that can help you to feel better.
It's okay, I'll just kill myself.
Killing yourself won't solve anything; think about the people you'll be leaving behind. Please try calling the suicide hotline if you're having these thoughts.