Caitlin says to Nash at the end of this episode "Boy, you sure know how to pick 'em" referring to the brazen Dr. Lorie Billings defiance of Nash. She pulls a gun on Nash, and then when she's disarmed, Lorie spits out she'll only do two years for her crimes. Lorie's a former flame of Nash, and like all those other Bad Girls (always attractive, professional women) of previous episodes, they have an intimate moment over dinner before Nash sets the trap.
The difference this time is that Nash is spoken for (he's got Caitlin). The possibility of a seduction, of a final roll in the hay with the Bad Girl isn't possible - with Caitlin around Nash can't really smolder. But there's still that incestuous quality about the relationship. The Bad Girl's love/hate of Nash is of a daughter rebelling against an authority figure. Nash is Big Daddy trying to tame an out of control daughter. But when Nash ultimately does take the Bad Girl down, it's no longer Boys against the Girls with Caitlin around.
This is similarly reflected in Nick's pangs of independence. Nick woos a Sugar Momma (doing follow-up studly duties with a dose of Viagra). The possibility of a matriarch keeping her stud muffin around is extinguished when she ups and dies (to which a sleazy Nick mistakes for oral sex when she dies in his lap). The Girls are given a chance, but they can't quite keep up with Nash and the Boys.
The Fallen Boy - Evan, still hasn't bottomed out yet. He's become a marginal cop, carousing with prostitutes, drunk on the job. Evan may be headed out of the show if this continues - perhaps a shocking Season Finale with Evan vindicating himself by dying heroically in the line of duty? It sure looks like it's heading that way, and remember, I mentioned it here first.
For more, see synopsis for Episode 85