Well, now you've done it. You used the word "sin" to describe an action and now all the Wrongplanet atheists are gonna come out to tell how there's no God and anyone who thinks so is a delusional idiot.
But to answer your question, in the eyes of the church (Catholic church, anyways) suicide and murder are essentially the same thing. In the eyes of PEOPLE, though, it's different. Suicide is a result of depression and sadness, and is to be pitied. But murder is a result of anger, hatred, jealousy or malice, and is NOT viewed sympathetically.
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Everything would be better if you were in charge.