The Varsity is first mentioned on page 20 when Jen says she has been going there a lot to watch old movies. Jen was there for the Bogart Festival. Eric says he was there for To Have and Have Not, which Jen says she also attended.
The Varsity is again mentioned when Jen writes to Eric in orange font about an S symbol being painted on the side of it. She also notes that Santana is showing at the Varisty when she writes in purple font.