Hello again Katherine,
Suicide is murder
Having said that, we must add that murder, suicide, or any other sin is not the deciding factor regarding salvation. A person's eternal security is determined by, and only by, their relationship to Jesus Christ (Ephesians 2:8-9).
If a person who is unsaved commits suicide, they have simply sent themselves to eternal punishment faster than they would have gone had they died a natural death. Regardless, they will be in eternal separation only because they have rejected Christ, not because they have committed suicide.
But what if a Christian commits suicide?
The Bible says that when we are in Christ, our salvation is guaranteed because His Spirit dwells in us (2 Corinthians 5:5). That same Spirit is put into the hearts of all those who believe in Jesus Christ (John 3:16; 1 John 5:13).
The Bible also makes it quite clear in Romans 8:38-39 that nothing can separate a Christian from Christ's love, not even suicide. If no "created thing" can separate us from the love of God, as the verse says, then no person (not even our own selves) can separate us from His love by any act that we do including suicide.
A Christian should exhibit the fruit of the Spirit (Galatians 5:22) & will be protected from sin as they abide in Christ (John 15:4).
However, if a Christian falls & commits the terrible sin of suicide, that sin would still be covered by Jesus' blood.
Christians are not immune to the despair that leads to suicide; the enemy is a great deceiver (John 8:44) who wants us to forget that victory is ours in Christ (John 16:33). Still, suicide is a very serious sin..
There is no circumstance which justifies a person, especially a Christian, to take his or her own life. We are supposed to die to self, not kill ourselves.
Sorrow over our sins or mistakes should lead us to repentance rather than self-harm so that we can be restored and not destroyed. It is God's heart to repair and restore that which is broken (Psalm 51:17; Isaiah 42:3; Matthew 12:20). Even when things look incredibly bleak and hopeless.
Moses murdered a soldier (we see him later on the Mt of Transfiguration) King David had Bathsheba's husband killed. Paul was the overseer of Stephen's & many other deaths. I'm pretty sure next to Jesus Himself. Paul is responsible for turning the most people to God.
Finally, there is only ONE unforgivable sin. Rejection of Gods grace found in the redemptive sin atoning sacrifice of Jesus the Christ = UNBELIEF.