Peter Facinelli Peter Facinelli

Monday's season finale of Nurse Jackie is not just a moment of reckoning for substance abuser Jackie, but also for Dr. Fitch Cooper, whose less-than-ethical behavior comes back to haunt him.

Peter Facinelli, who plays Coop, likens his character to "a puppy in a room full of people who don't like dogs." Though Coop is for sure a doofus, Facinelli says he never plays the part for laughs. Instead, he says, "the more dramatic I try to be, the funnier it is."

When Sam discovers that Coop slept with his girlfriend, the not-so-good doctor compounds the deception by telling Sam she'd rather be with a doctor than a nurse anyway. This news all but obliterates their nascent friendship (which spawned this awesome/awful rap) and leaves both men in a fragile state by the episode's end.

"He tries so hard to fit in, and he really wants people to like him, and he wants to believe that people do, but there's always a part of him that goes home and cries himself to sleep," Facinelli says.

Coop's complicated relationship with Jackie (Edie Falco) certainly won't be resolved by season's end, but he will have a small role in her downfall. "It's just more fodder for him to get attention from her," he says. "He's become the kid in third grade who has a crush on a girl so he pulls her pigtails."

Also in the season finale: Kevin and O'Hara team up in the face of incriminating evidence, two couples make important decisions, "God" returns, and it's Thor to the rescue!

The season finale of Nurse Jackie is Monday at 10/9c on Showtime.