We have gotten confirmation of the McAbby ship is in season 12's "Semper Fortis".
McGeek: I know what you're thinking of doing and I just want you to know that I think it's premature.
Abby: Okay, McGee, I know that we used to... and we don't anymore, and it's been a long time. But, uh, this is kind of private and sort of none of your business, so...
McGee: Abby, come on.
Abby: If I want to break up with Burt, that is my decision.
This is in reference to an earlier conversation, referring to Burt as "Mr. Two Months". Later turns into this conversation.
McGee: All right. Well you should probably know that Abby and I used to date?
Bishop: Ew. Like, each other?
Bishop: Wait - isn't that a violation of rule 12, never date a....
McGee: It was a long time ago. After we'd broken up, one night I went to her lab. Found a scribbled piece paper; a list. Potential boyfriends had to fulfill certain conditions by a pre-arranged date or else, goodbye.
Bishop: Such as.
McGee: Things started off relatively normal: opening the door for her, flowers, putting the seat down. Then around number 8, it gets uh...
Bishop: Does she know you have these?
McGee: Yeah she wasn't happy when she found out.
Bishop: These are all very... specific.
Bishop: These ideas apply to you?
McGee: No those rules weren't in place when we were together. At least I don't think so.
Bishop: What's with the two month cutoff?
??: Abby's sabotaging herself. I've seen stuff like this before.
??: We have to talk to her.
First on-air confirmation of the relationship that happened in Season 1, ending early season 2. Of all the stolen glances and moments the two shared. And McGee's possessiveness later on. Ever since then, Abby has been a serial dater.