Complex sentence: On returning home, Dorian notices that the portrait has changed; his wish has been realised, and the portrait bears a subtle sneer, and will age with each of his sins, while he remains youthful and unchanged.
Split into simpler sentences: On returning home, Dorian notices his portrait has changed; his wish has been realised, and the portrait bears a subtle sneer. It will age with each of his sins, while he remains youthful and unchanged.