Obviously a suicide is the opposite of a martyr.

A martyr is a man who cares so much for something outside him, that he forgets his own personal life.

A suicide is a man who cares so little for anything outside him, that he wants to see the last of everything.

One wants something to begin: the other wants everything to end.

In other words, the martyr is noble, exactly because (however he renounces the world or execrates all humanity) he confesses this ultimate link with life; he sets his heart outside himself: he dies that something may live.