Complex sentence: Instead of belief in God, Stavrogin has rationality, materialism, self-reliance and egoism, but the sensual ardour of his childhood and youth, over-stimulated by his teacher Stepan Trofimovich, has never left him.
Split into simpler sentences: Instead of belief in God, Stavrogin has rationality, materialism, self-reliance and egoism. The ardour of sensual yearning, over-stimulated by Stepan Trofimovich in his childhood and youth, has never left him.