It was in Plan B (Season 2, Episode 22)
some quotes from that episode
Ray: [about Marty and Nicole] Hey, it could work.
Marty Deeks: Yeah, maybe if things were different. Ray, she doesn't even know who I am.
Ray: Does Wikipedia know who you are?
Marty Deeks: Okay, easy. She's just my partner.
Kensi Blye: What are you guys talking about?
Marty Deeks: Nothing. Just discussing the uh, pertinent details of the case.
Kensi Blye: Okay.
Ray: Promise me that phone call, Marty. Deeks: (embarrassed) No. Ray: I wanna hear how your thing turns out with Wikipedia. (Deeks laughs and shakes his head) You know you owe me that much! (hurries off) Deeks: (hollering after him) There is no thing!
Kensi: Planning on calling Ray anytime soon? Deeks: (firmly) No. No, I'm not. (pauses) Why do you ask? Kensi: Just, when you do, tell him Wikipedia says hi. Deeks: (smiling and shaking his head) I'll do that. Kensi: Oh, and, um...(strides up close to him)...I'm glad our "thing" is working out. (grins and walks away) Deeks: (mutters to himself) No "thing." (calls after her) There is no "thing!"
and here is the picture that confirmed it
I mean that he is back
since it is from a writers twitter I was not sure how to post it 
I know, I know I have a present tv show board myself, but this is very confusing from time to time 
we are just nuts for them 
