First, let me clearly say that suicide is the most selfish act a person can commit. Thse who commit suicide leave others behind to feel sorrow and guilt over the persons suicide... "could we have done more?"; "Did I do something to push him along that path?"; etc. Suicides leave devestation in the hearts of those who loved them.
Still, I would say that the vast majority of suicides are by people who are not in their right minds. I have been depressed and delusional to the point that I contemplated suicide after renouncing my faith in Jesus... talk about not in your right mind!!! But something in my heart would not let me do that to my parents, who loved me. I truly believe that God was in my heart drawing me back from the edge even at that point. Fortunately, my heart won out over my mind and I never tried, even though there were several times I sat there with the shotgun in my lap thinking about it, and once I even had the gun in my mouth and the safety off!
God drew me back, but that doesn't mean that someone in a different situation might have their distorted minds win out over their saved heart. I believe that it is a horrendous sin, but all of a Christians sins, both past, present, and future, are forgiven at the moment they receive Jesus Christ. Their spirits/souls are transformed and born anew, a new creation. I am living proof that someone who is truly born again can go all the way to the edge, but not cross the line. I believe that if my parents had not been alive at that time I would have done it, because in my mind at that time they were the only ones who would be terribly hurt by it (although I know better now). So I beieve that it is possible for someone who is truly born again to commit suicide.
Now comes the question, particularly in my case because I actually RENOUNCED my salvation some time before seriously contemplating suicide... would I have been lost if I had went through with it? After all, the Bible does have some passages that indicate that it is possible for a believer to fall away. I have to say that I honestly don't know for sure, but I think I would have been lost because I had actually gone so far as to renounce my salvation before God. Thanks be to God that He did not let me go and brought me back not only from the edge of suicide but also from the depths of my despair and the power that my delusion had over me. I have since recommitted my life to Jesus, and I believe that He has forgiven me and is again active in my life.
But in most cases, I think it should be obvious from the fact that ALL our sins, even the ones we do after coming to Christ, are forgiven by God as we partake of the benefits of the cross by trusting in Jesus as our Savior and Lord. NO!!! I do not believe that people who commit suicide go to hell for that sin... there is only one sin that condemns to hell, and that is rejection of Jesus Christ as your Savior and Lord.
Paul writes about the blessed security the believer has at the end of Romans 8, and I will leave you with that:
Rom 8:38-39 NIV For I am convinced that neither death nor life, neither angels nor demons, neither the present nor the future, nor any powers, (39) neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord.