The Bible doesn't actually say anything about suicide. People are stringing together interpretations of different pieces to argue that commiting suicide is a sin that condemns one to hell.
People tend to believe suicide is a sin based on the Biblical statement that murder is sin, and they equate suicide to self-murder. I'm not sure I buy that because it's different to take a life against someone's will. I would claim that euthanasia and suicide both fall into a different category than murder because in those cases the person wants to die.
Even if you believe that suicide is a sin, it's still a huge leap to say someone is necessarily condemned to hell for it, because sins can be forgiven. Some people claim that suicide is a special sin that can't be forgiven, I won't get into that argument here but it sounds convoluted to me. I'm more inclined to believe that God (if He exists) would be loving and merciful to people who's suffering was so great that they chose to commit suicide in order to escape the pain.