He is portrayed by Ian Gilligan.
While Blaine is singing Barely Breathing, he is seen sitting in the choir room by himself, on Facebook on his cell phone. Blaine scrolls through Facebook, before he pokes "Eli.C" on Facebook. A chat is started between the two, with Eli starting off the conversation by saying, "What's up, sexy?". After this, Blaine smiles slightly before Eli messages him again with, "You want to come over?" Blaine looks contemplative, before standing up and walking out of the choir room. It is presumed that Blaine is walking out with the intention of meeting Eli.
Later in the episode, Blaine confesses to Kurt, after Kurt asks why Blaine has been so upset despite the fact that they are seeing each other for the first time in weeks, that he was "with someone." Kurt asks if the person was Sebastian, and Blaine says that it wasn't but it "Didn't mean anything. It was just a hookup, okay?" Kurt once again asks who it was, to which Blaine replies that it doesn't matter who it was with. The person Blaine is referring to is Eli.
Blaine and Eli's encounter was severely dismissed by Kurt when Blaine was trying to explain what had really happened that night. Kurt refuses to find out what exactly happened between Blaine and the guy he hooked up with" - and Kurt knows it is possible that Blaine only made out with him, but he doesn't want to hear it, whatever it is.
In this episode, when Sam confronts Blaine and persuades him not to leave McKinley and transfer back to Dalton because of his broken relationship with Kurt, Sam asks Blaine what happened the night with him and Eli. A flashback shows Blaine looking saddened after hooking up with Eli. Eli stands, out of focus, in the background, asking Blaine if he's OK. When Blaine answers that he isn't, Eli asks if it's because he doesn't look like his profile picture. It is strange that he says this, since his profile picture is a lighthouse.
Kurt states that he and Blaine haven't taken an STD test since Blaine's affair with Eli.C.
Blaine and Eli have most likely met prior to The Break-Up, seeing as they were Facebook friends at the beginning of the episode. Their relationship is flirtatious, at least on Eli's side, and they hooked up at some point in the episode, before Blaine surprised Kurt in New York. The hook-up most likely took place after the Barely Breathing performance.