He is Carly's crush (love interest) for that episode. It has been rumored by fans that he'll return, but it's unlikely.
Adam makes his only appearance on the iCarly TV special iStart a Fanwar. He is Carly's love interest for that episode, and obviously likes Carly since he asks her out and comes to Webicon just to see her (see "Cadam"). He is seemingly jealous of Freddie, believing that he and Carly have a "thing" going on due to the Creddie forums he saw, where the Creddiers were saying stuff about Carly and Freddie, and when Sam said that, "Carly and Freddie are deeply in love." He gets attacked by the Creddie shippers in the end, as they believe he was a "Creddie killer" and that he took Carly away from Freddie. It is implied he is a Seddie shipper, with his dislike of Creddie, smiling when Sam admitted Carly and Freddie weren't dating, and said "Seddie, got it."