No, he didn't divorce her because the son wanted to know his bio family. Read it again. He divorced her because she lied to him throughout their marriage, telling him she didn't know who the bio father was. She let him adopt the boy. Then, without ever mentioning it to her husband and her son's adoptive father, she told the son who his bio dad was (after lying to her husband for years about not knowing). That affected his level of trust with her hugely. I don't blame him. Imagine someone lying to you about your child for years, then going behind your back to tell that info to your child. Everything in your life changes. At the very least, he should have been part of the discussion about revealing the bio father's identity and he should have been told.
He didn't divorce her bc the kid wanted to know his family, he divorced her bc she lied to him for years about their son and then went behind his back to damage his relationship with the kid. NTA