Brothers Plus

From Yaoi Is Life:

Watanabe Chris is a high school teacher.
When his father remarries, he finds himself with an English stepbrother named Wataru. Shortly after Wataru transfers to the school that Chris works at, their parents die suddenly in an accident. Chris and Wataru begin to live together, and before long they fall in love.
Wataru enters his second year of college still living his happily-ever-after with Chris.

At the same time, Wataru's childhood best friend and former suitor, the cross-dressing Rei, is falling for Yamada, who's always secretly had a crush on Chris...!