2x11 need to know, it's the same episode that they consumate the relationship and the same episode that Stacy leaves in.
here's the dialogue: Stacy [turns to go]: Yeah. [turns back] What was Greg like after I left? Cuddy: Uh, an egomaniacal narcissistic pain in the ass. Same as before আপনি left. Stacy: Do আপনি think he's capable of having a real relationship? Cuddy: What happened in Baltimore? Stacy: Nothing. Cuddy: Right. Stacy: Maybe something. Cuddy [wincing with eyes closed]: Right. Stacy: Technically, most of the something happened after Baltimore. Cuddy: Oh God, Stacy... Stacy: I don't know what to do. Cuddy: Are আপনি seriously thinking about leaving Mark? Stacy: No. I don't know. I can't. Cuddy: And আপনি want me to tell আপনি it's okay? Stacy: It wasn't all bad with Greg. I was with him for a reason. Cuddy: আপনি left him for a reason. Stacy: I could swear I remember him being fun. [Cuddy smiles apologetically but says nothing.]
