Suicide - The unpardonable sin?

I hear that if a person kills themselves, then they are lost. I'm told that suicide is the 'un-pardonable sin'.
Why? Well, because... how can they repent of that sin?

Some tell me that, and others tell me that Jesus died once for all sins.
Both past and future. That, of course, might lead one to think that the sin of suicide was already forgiven. But, if that's true, then who has to worry about anything???

But, there is still that pesky word, 'repentance'... how does a dead person repent?
How do they approach the Throne of God to say, "I'm sorry"?

In my bible, I see that Christ is to be our 'advocate'... that His death was to cover our past sins. And, to make a way for us to repent of future sins, by seeking God's forgiveness. But, if one kills themselves...what then? Are we already forgiven or is that the sin that can't be forgiven?

Phil
"on fire for the Lord, or on fire for your sins... your choice"