Complex sentence: Macbeth becomes a tyrant, brutally stamping out any real or perceived threats to his power; he believes himself to be "in blood stepp'd in so far, that, returning were as tedious as go o'er".
Split into simpler sentences: Macbeth becomes a tyrant, brutally stamping out any real or perceived threats to his power. He believes himself to be beyond redemption, "in blood stepp'd in so far, that, returning were as tedious as go o'er".