That's what I was thinking too. If I remember correctly, isn't he some sort of CEO or someone in a high position in the company? If so, I believe he may have focus too much of his time and effort in the company than his own family. And maybe he found out in the worst way possible or wished that she had divorced or at least talked to him before continuously meeting up with this person. But since she didn't do that, I guess it broke him emotionally.
Maybe, just maybe, he was in love with her.
You're right, it isn't. Unfortunately, realistically, it's a common thing that generally happens in divorce/separated families. I have never experienced it before let alone have much knowledge on it, but I have heard that it's one of the major concerns when a family goes through a divorce, especially if it went downhill, that parents generally neglect and or abuse the kid that looks like their former spouse.
It's horrible indeed, but mentally and or emotionally, it must be tough for them to get over the emotions they have felt for the other and it's unfortunate that not only does the kid looks like their former partner, but they get backhand of everything.
His mom is a piece of shit just like his dad.
#-.-)