Who is Arch Carroll from Black Friday and what is their importance?

A New York cop and director of the anti-terrorism team, Carroll lost his wife, Nora, three years ago. He has spent his time since then raising his four children, drinking too much and taking incredible risks at work. He says that he realizes what he's doing, but seems powerless to stop. He's seen no one socially since his wife's death and is attracted to Caitlin Dillon. They make love one night in Carroll's apartment and he wants to bring her home to meet his children, but they are reluctant.