Summer,
Alas, it doesn't only apply to men...my exgf was the culprit in my life. It's the way people choose to live and interact in the world. I know you know this, but I had to speak up for the men.
The only criteria is that it's a person who is capable of putting on blinders and moving forward that way. It's incredible, isn't it? My ex had herself completely convinced that she wasn't doing anything remotely deceitful, all the while maintaining contact with her "affair". Sure, I sorta knew about it in terms of it having happened, but the other person's partner did not. Somehow my exgf thought it was okay to continue the relationship, and foster it, so long as it didn't involve sex. Yeah, right. Phooey. I wanted her to discontinue the contact, and I could feel it when she'd been in contact, but she denied it most of the time until much further down the road.
All the while she kept turning it around and making it about my "hang-up" and "wanting to change the past" and me being "judgmental". I put up with it for a long time (AKA abandoned myself), that nagging gut feeling and being told that I had trust issues and needed to "LET GO."
Well, I did let go. I let go of her and she's still p*ssed. NOT.MY.PROBLEM.ANYMORE.
Cheers to you SP, wishing you easing of your pain and a future of healthy self-centeredness.
Hugs,
posie