Kore kara Hajimaru Koi wo Oshiete

Akira only pretended to marry her childhood friend Sotaro to please her sick grandmother. However, everyone around her took the fake marriage seriously, and they ended up living together. Akira barely remembers Sotaro, even though they have known each other since childhood. And then Akira finds out that Sotaro is her new college professor... This is the an extremely sweet story of doki-doki love!
(Source: Shogakukan, translated)
Included one-shots:
Volume 2: Ame dake ga Shitteiru
Volume 4: Watashi no Unmei 7-kakan