Gustin will play Sebastian, a gay student at Dalton Academy who will come between Kurt and Blaine, played by Chris Colfer and Darren Criss, respectively. Sebastian is described as the male version of Santana (Naya Rivera) and this season's villain.
Also on the upcoming episode, as McKinley High prepares to put on the Leonard Bernstein-Stephen Sondheim-Arthur Laurents classic West Side Story, the students will perform covers of "America" and "A Boy Like That."
The characters of Santana (Rivera), Quinn (Dianna Agron), Brittany (Heather Morris), Puck (Mark Salling) and Mike (Harry Shum, Jr.) will perform in "America"; and Santana will join Rachel (Lea Michele) for "A Boy Like That."
Here's how Fox describes the "My First Time" episode: "Under Artie’s (Kevin McHale) directorial leadership, the kids prepare to perform the school musical West Side Story. Meanwhile, Finn (Cory Monteith) meets with a recruiter, and Coach Bieste (Dot-Marie Jones) has an admirer."
"Glee" airs Tuesday nights on Fox at 8 PM ET.