@versub the first page of the second chapter the letter says "this is the first letter I've written you since we divorced 18 years ago. The enclosed photo is of your 18 year old daughter" so unless she is lying, AND you are spoiling the story, its his BIOLOGICAL, aka blood-related, daughter.
@fivestarninja there is the possibility of the mc not being actually related to the father given his hair color, but that's too much drama... so probably not.
they arent able to meet, the two become a couple and do it,yes they do it, it is after that he meets his mother,recent chapter ended with that much only