Unmei wa Maigo

Taizou and Ikuto, only 1 year apart, have been together since childhood. They went to the same kindergarten, the same middle school, and even the same high school. Despite being younger, it's thanks to Ikuto that Taizou managed to pass his college entrance exam so that they could go to the same school together. However, in the year that they're apart, Ikuto drifts away and ends up going to a different school. Taizou, oblivious to Ikuto's feelings, chases after him to find out what happened.

(Source: Core Magazine, translated)