That was my thought while reading it. Why didn't they tell him 10 years ago? The title is worded like the dad didn't learn about her infidelity until recently, but he's known since it happened, she even moved out to see the other dude, and they got back together months later.

None of this is new information. Why wait until some argument to blow up about it? The kid should have known about the time he hit his teenage years that he has another father out there, so he could make his own choice about seeking him out.

If the parents hadn't gotten into a huge argument, were they just never going to tell him? Or maybe that's what the argument was about? One of them wanted to tell and the other didn't?

It's just so odd.