The MC has a crush on his Senpai at High School, she obviously liked him and was clingy around him like him any cliche Manga Protagonist but this time the “Heroine” stopped trying to pursue him and lived her own life, got married and had kids. The MC was too cowardly and didn’t speak up thus loosing her. Now he’s taking care of her kid who has a crush on him as a Teacher. Now he found a new love, you guessed it, the Teacher. Though the MC did grow up a bit from taking care of kids. But still holds that indecisive cowardly personality. Which made me be like WTF. What ruined it for me was when his Ex/Senpai becomes a character in the series as well, I liked it when she was a background character. Because now it’s just awkward reading when you know this.