Complex sentence: Lupin attacks Harry with his wand, smashing him into a wall, and leaves in a rage provoked by Harry, though he inevitably sees the truth in Harry's words and returns to Tonks's side.
Split into simpler sentences: Lupin attacks Harry with his wand, smashing him into a wall, and leaves in a rage. Inevitably, he recognized the truth in Harry's words and returns to Tonks's side.