Complex sentence: He and Mary remained together in Collioure until her death in 1998, but he continued to work on his naval novels, spending the winter of 1998--1999 at Trinity College, Dublin, which had awarded him an honorary doctorate in 1997.
Split into simpler sentences: He and Mary remained together in Collioure until her death in 1998. He continued to work on his naval novels, spending the winter of 1998--1999 at Trinity College, Dublin, which had awarded him an honorary doctorate in 1997.