Complex sentence: Who was R.M.-the boy who rejected him during a mountain-top tryst in high school, which broke his heart and convinced Stewart to live in exile in the closet for the rest of his life.
Split into simpler sentences: Who was R.M.-the boy who rejected him during a mountain-top tryst in high school and broke his heart. In later life he grew more guarded remained in the closet for the rest of his life.