Actually...I have a bit different perspective on this.
She cheated on him. Cheating on your lover/spouse is one of the worst things a human being can do to another human being, in my estimation. It's the ultimate betrayal.
Therefore, I can see why he lost it. I can imagine attacking my spouse if he told me he had cheated on me. Also, it sounds like she wasn't really hurt, there is no mention of any real injuries. In addition, she refused to testify against him.
And I'm a former abused woman, spent 4 unfortunate years with a man who sometimes got physically abusive when he was drunk, put me in the emergency room twice. I never cheated on him, good Lord, he would have killed me.
I just don't think this guy sounds like a real monster. It really hurts when someone cheats on you, it's like getting stabbed in the heart. Makes people go berserk sometimes, even good people.
He's on probation and getting domestic violence counseling. Sounds about right to me. Now maybe he can find a woman he really loves HIM, and not his money.