Re: Why do women do it?
Statistically speaking, more men cheat than women do in relationships, so I find your question interesting. I'll take a stab at it. Short answer, women cheat for emotional reasons.
My married ex-AP (male) started flirting/pursing me over email, with the occasional confession that he "wished things could be different" (ie date me). For a year and a half. I took the energy home and tried desperately to make my marriage better (read: sex at home).
Despite being married to a guy who is extremely selfish, disrespectful,poor hygiene, sometimes borderline nuts, not even a very good dad, frankly, I didn't pursue anything physical with the this guy - until my husband (despite noticing the improvements in me but not improving himself at all) turned even meaner, which I didn't think was possible (no, he didn't know, one benefit of being married to a narc. person who's had their own affairs is that they will never suspect you...)
It was at that point, with the mental decision in my head that I was headed for divorce anyway, that I moved from an EA to a PA, but it was really short lived, because the comparison between being with this other guy and the meanness at home was too heartbreaking for me personally. He was just using me since he wasn't getting enough sex or attention at home (like many of your male stories here) but admitted his marriage wasn't toxic like mine - it was "good enough" and he was never leaving, of course.
Yes, some people are serial cheaters. Some people just make mistakes. Some people have experiences that change their lives and tell them finally they need to get out of both situations. Mine was the last.
Hope that helps.