I think cheating on a guy is worse and beating on a chick is worse.
Mostly because if a guy beats a woman, it's more likely to be more severe. Like, I'm never afraid of my wife beating me, unless she had a significant weapon and the element of surprise, but if I beat her I could put her in the hospital with my bare hands.
I would be more worried about her cheating on me.
The mental gymnastics needed to explain this is pretty impressive. Have you considered entering the mental Olympics?