Complex sentence: A formative event was his singing performance at his school's annual Speech Night in December 1926--none of his family were present, and the sense of loneliness he felt that night remained with him throughout his life.
Split into simpler sentences: A formative event was his singing performance at his school's annual Speech Night in December 1926. None of his family were present, and the sense of loneliness he felt that night remained with him throughout his life.