Complex sentence: He was an intensely private, eccentric and reclusive man, and became more pessimistic as he got older, especially after the death of his father, when his gallery to fall into disrepair and neglect.
Split into simpler sentences: He was an intensely private, eccentric and reclusive man. He became more pessimistic and morose as he got older, especially after the death of his father, after which his gallery fell into disrepair and neglect.