Complex sentence: Lee and PIL moved to New York City, were they stayed during 1980 and 1981, after which she moved back to London and met and fell in love with Gareth Sager who she would have a child with.
Split into simpler sentences: Lee and PIL moved to New York City, were they stayed during 1980 and 1981. She moved back to London and met and fell in love with Gareth Sager who she would have a child with.