He was born and bred in Boston (Dorchester). He joined Boston PD and worked his way up to join the gang unit. Moved to NYC when his wife had an ailing family member she wanted to be close to. Then he joined NYPD and switched over to the narc unit. He and his ex wife were divorced for just a bit and then she was shot in a robber gone wrong. He had his suspicions it wasn't so simple ad went to a higher power to get some answers and in exchange helps them out. So he's a narc detective with a side of dirty.
I'm trying to think of how they could've met. Maybe she was brought in on drug charges one night?