Sex Is Zero 2 (movie, 2007)

'Veteran' student Eun-shik and prom queen, swimming champ Kyung-ah are a notorious couple at the campus. While their relationship has been solid for three years, Eun-shik struggles to proceed to the 'next step' with Kyung-ah, and despite the help and support of his friends, does not manage to get her into bed. Eun-shik fears that Kyung-ah will turn her back on him and is determined to get her back...