Complex sentence: Esmeraude refuses, and leaves Rubeus in the unstable spaceship, saying he's failed too many times to be of any more use; in the end, his obsession with killing Chibiusa is his downfall.
Split into simpler sentences: Esmeraude refuses, and leaves Rubeus in the unstable spaceship saying he's failed too many times to be of any more use. In the end, his obsession with killing Chibiusa is his downfall.