Suicide always involves more than one person.

Suicide, as everyone knows, casts a shadow over those it leaves behind. But according to Freud, the act of suicide always involves more than one person. Maybe that is one reason why suicide is classified as a crime. Maybe, too, that is why biographies of someone like Sylvia Plath always take on the aura of hunt the culprit: not because, as is most often assumed, someone – usually Ted Hughes – must be held accountable for her death, but because there is an unacknowledged crime calling out to be uncovered, another body to be found.

Source http://www.lrb.co.uk/v24/n16/jacqueline-rose/this-is-not-a-biography