The (dead) dad was cheating. It was mentioned in previous flashbacks that was the reason he stopped being interested in the MC. b1tch1ng
But here it was mentionned the dead dad never did penetration with MC to begin with. And despite that he still had frequent sexual activity with MC and planning to get married. So that doesnt really add up with what you said unless im missing somethingq
I hope we will find out why sangwoo's dad lost interest in penetration after sangwoo's birth.
Also like why is Sangwoo throwing the MC at other alphas... it's kind of odd especially when he was already breaking the MC's mind without all this