"If he was happy with her gone and wanted to be single as some suggest, why be mad she was leaving him?"
Easy answer for that question. We see it time and time again, with family annihilators.
>>>>FREEDOM from responsibilities. He didn't want his pregnant wife to leave the home, have their 3rd child, then file for divorce and child support.
He would NEVER be truly 'single', as long as he had 3 young children and an ex wife. And it is hard to start a 'new life' with so much baggage, all with your last name, calling, req.esting things, making arrangements for health insurance and holidays, and being NEEDY.
"If she made more money then he would maybe not have to pay as much support right..."
But the only way she would owe more money would be if he split the custody time in half. How is he going to do that and continue working and dating? He'd be devoting all of his free time to childcare and that was not what he envisioned in his 'new life.'