Complex sentence: A few years afterwards, Peter began a long relationship with a woman named Eleanor Archdeacon, of whom little is known, but whom he sometimes referred to as his wife, and by whom he had at least six children.
Split into simpler sentences: A few years afterwards, Peter began a long relationship with a woman named Eleanor Archdeacon. Little is known about her but he sometimes referred to her as his wife, and they had at least six children.