Seiji Sanada, a 30-year-old wage slave, woke up one morning and had time leaped back to the spring of his sophomore year of high school. Seiji, who had long regretted graduating without confessing to his beloved world history teacher, Haruka Hiiragi, resolved that this time, he’d confess to her. Her response was... An astonishing ‘Okay’?!?!?!?! The two of them began discretely dating. It was supposed to be the start of their vie en rose... but Hiiragi-sensei is a woman so sweet, she’ll spoil her man rotten!!! A super flirtatious rose-colored school life begins!!! e2l3j
Source: MANGA UP! Global
5 Volumes (Complete)

Ending made no sense whatsoever. It was very poorly written.
Her breaking up with him really did make no sense. Even the sister wasn't rejecting the idea of them dating but she still did it anyways. And wtf was tht 10 yr timeskip. Bruh make it a little less, 10 yrs is too much considering she's already past her mid 30s