Overwhelming urge to beat...?

the **** out of the "other woman". My husband had an affair months ago and we are doing great in our marriage...better than ever. The other woman knew he was marriage w/3 kids and she still pursued him. I'm not excusing his part, he was wrong, but this feeling of causing her pain is getting more intense. I've never hit anyone in my life but I just want to slug that little tramp. Why is this? Why would it be getting worse as time goes on rather than diminishing? Especially seeing my husband and I are doing awesome in our relationship. Serious answers only plz!