OL In Her Prime: Sucking During Cohabitation(2011)

Office worker Misako lives with her boyfriend Ken. As they near their goal of raising money for their wedding, the couple find themselves in a slump. One day, Misako receives news of a class reunion. She had a crush on her high school teacher, Shima Masayuki, and when she meets him again at the after-party, they begin a relationship.