Yes. It is an unforgivable sin. Killing yourself is a sin and the reason it is unforgivable is because once you are dead you can't repent.
I would never committ suicide regardless of how bad my life is going. There are only 2 possible things that could happen and both are bad. Either you die and go to hell or you die and become nothingness.
The only suicide I feel is halfway justifable is if you are saving somebody else's life but you know that doing that would mean you would die, or if you are going to be tortured to death. If you know you will die you might as well not give them the satisfaction of torturing you.