Nick + Nettie
Were they having a fling while he was married? They knew each other for a while.
"just panties, what else do I need?"
Poseidon Adventure
You didn't listen closely enough to their conversations (in their scenes together throughout the film), I'm afraid.
Nettie was their baby sitter (and still a teenager, at the time) who had a secret crush on the then-married Nick. Nettie didn't open up to Nick about her feelings until she, subsequent to Nick's wife's suicide, visited him in prison.
Nick had only been grief sticken when he got wind of his wife's death, but was later stung to learn from Nettie (during the prison visit) that Mrs Bianco had been sleeping with one of his old cronies, Rizzo, while Nick was rotting in jail.
Secret Message, HERE!-->CONGRATULATIONS!!! You've discovered the Secret Message!