Okusama wa Joshikousei (2005)

Summary

Asami Onohara is a seventeen-year old high-school student with a secret which has not been revealed to anyone: She is already married. Her husband, Kyosuke Ichimaru, is a Physics teacher in the same high school as her. However, even though they are officially a married couple, Asami's father forbids them to have any sexual contact until after Asami has graduated. Asami has to hide the fact that she is married to Kyosuke while trying desperately to further their relationship, and it does not help when there are so many interferences and obstacles from her father and other third parties.

(Source: Anime News Network)