Even if the marriage was already ruined, is the other woman still considered a "homewrecker"?

I was wondering if a man was cheating on his wife and was already not happy with her, is the other woman still considered a homewrecker if she stays with him in a relationship? What if he lied to her about his marital status and she didn't know the whole truth, is she still at fault and should the wife take it all out on her if she's innocent victim? I've seem alot of wives who would mainly take it out on the woman all the time and not their own husband, cuz it takes two to tango instead of one.