As a child that has lost her father and that has been raised by a single mom I can assure you that it's not that easy. The fear of being left alone or abandoned can only be understood by someone who went through it.
You explained it perfectly
I was also raised by a single mother, my father abandoned me for a new family when I was 3 years old. My mother always gave me liberty and explained everything I know. And, even thought I was pained because my father abandoned and my mother never hid the true from me. I get that the father can be overprotective and want to shield the kid, but he still has to explain that he is his father and that he will always be there for him and that the other guy is his boyfriend, and that his boyfriend will never take his place in his heart.
I loved the first story, I loved how the uke was a little kinky. I did not like the second story because of the father and the kid. As a father he should teach his son that he loves him a lot, but that what he feels for Kazuki is a different kind of love and that the seme will not “steal” him. He should definitely not go along with his son whims and spoil him, that’s so bad for a kid.