Complex sentence: J is largely without a partner, after Agent L (from the first film) decided to return to her former life decided to return to her life working in a morque and subsequent partners have not lived up to J's professional standards.
Split into simpler sentences: J is largely without a partner, after Agent L (from the first film) decided to return to her former life working in a morque. Since then, subsequent partners have not lived up to J's professional standards.