Sea of Love (movie, 1989)

Seen-it-all New York detective Frank Keller is unsettled - he has done twenty years on the force and could retire, and he hasn't come to terms with his wife leaving him for a colleague. Joining up with an officer from another part of town to investigate a series of murders linked by the lonely hearts columns he finds he is getting seriously and possibly dangerously involved with Helen, one of the main suspects.