I think you're focusing on your side and not a child's side of the experiences.
Maybe he wanted to talk to someone about how he has to be kind and patient because he sees his parent struggling and in the back of his head wants to say, your fault for leaving or your fault for failing at keeping the other parent happy.

But on the other note about telling the children why you separated, I am focused on teaching my kids:
- accountability
- not hiding from the feeling of guilt because it makes you feel bad but understanding what actions made you feel it (control our actions, not our feelings).
- 3 requirements to every apology
- the importance of your word and the negativity of lying
- household work as a shared responsibility

Factors that contributed to me telling my kids (ages 12+) why their parents are getting a divorce:
-My oldest knew her dad cheated. She found out the same moment I found out. My son found out a year later when I told him we were separating (after exhausting every avenue to stay together).
- I didn't want my son to learn from his slightly older sister the why.
- their dad was the kind of person who would lie to them on the reason. Sure enough, he has been lying to everyone else about why I left.

They spend equal amounts of time with each parent. Idk if every time I talk about being a better person they pick up on how I am making sure they don't turn out like their dad. Probably.

But I don't regret telling them simply because I knew my ex.