Hey, sorry to ruined the wholesome atmosphere but, since the author stated that our MC is around 36 yo, and it's been 17 years since our MC and fmc broke up. They'll be 19 yo that time.
And considering the daughter's school level. She is now on middle school so, her age is probably at minimum 12 yo up to 16 yo.
So probably the child's not really that long to be born before they broke up?.
Well it's just a speculation but, this is my theory too, so it might ended up as spoiler.
Maybe She has a Family circumstances that she needed to go far far away from him, that's why she broke up With him. Because he mentioned that She ghosted our Mc with no way to contact each other.
Or some reason.