Is suicide a unforgivable sin

Suicide in and of itself is not a sin. It is the reason behind the suicide that creates the sin or lack of it. In particular, I speak of people who commit suicide to say to someone "look what you made me do." This does a harm for which, if you are successful in suicide, you cannot make amends. That, and other spiteful motives, are where you step into sin. I will also say that people who commit suicide out of unhappiness are making a mistake. Unhappiness is a temporary state of mind which can be overcome at least to some extent and perhaps completely. The only people who MIGHT be justified are those suffering a fatal and painful disease and are certain to die soon anyway.