Other than that the Bible doesn't say much about suicide. Basically Christians believe that suicide is wrong because you are taking a life, murdering yourself. And murder breaks the 10 commandments. It was Saint Augustine who really developed the theology of suicide as a grievous, cardinal sin. And his thinking went something like this.
Murder is a sin.
Whenever you die with an unrepented sin active in your life, you go to Hell. A person who practices suicide murders and doesn't get the chance to repent of his sin. Therefore, he goes to Hell. Augustine and his followers got at least a couple of things wrong here, brilliant as they were. Number one, forgiveness is not something that gets divvied out a little at a time after each sin is repented.