Behold, the Reasoning of Oprah. Men who cheat are dishonoring their vows, women who cheat are making a anguished plea. Of course she would sleep around on such a cad.
Hey, here's a thought ... They were BOTH amoral adulterers.
A man who deceptively takes marriage vows with no intention of keeping them - even as he takes the vows on the alter - certainly ranks as the prime villian to me.
Diana's subsequent behavior was a reaction to this ultimate betrayal of her trust. She was not the first offender here.
That said, you are correct - they were both amoral adulterers. And I happily defer to the Almighty to make the ultimate judgement.