Absolutely not and I don't believe it is a sin either.
I think few people believe this these days.
Really? Its the ultimate act of selfishness and trying to destroy God's will. Its a sin but I'm not sure if it ends in eternal seperation from God.
I really don't think suicide is the "ultimate" act of selfishness.
Those that committ suicide are not stable. I don't believe (and neither does the Church, by the way) that God punishes those that aren't able to think rationally.
So what about the 9/11 hijackers?