I can offer up my experience if it helps shed any light.
I had an affair with a married man at the age of 21. I had run away from home at the age of 17 (father physically and sexually abusive). I had been kept at home my whole life as part of my father's tightly-controlled bubble (never went to school), so had zero friends, and zero experience with other people.
I got a simple job and spent the 4 years from 17-21 in a kind of shell-shocked fog, trying to deal with the world (which I found terrifying), crying in bathrooms, and speaking to nobody.
I began interacting with people online as I felt 'safer', and it was much easier than face-to-face. And it was there, I met MM.
He was the first person to show me what I thought was love, plain and simple. I would have done anything for him, died for him, because he was the only person I'd ever met who seemed to care about me at all.
He told me he was only with his wife for the kids, that she did not want a "passionate" (his words) relationship, and didn't love him, that she was also just staying for the kids.
I fell for it hook, line, and sinker. I know now that this is a classic spun story, but at the time I had never heard it before, had no concept of cheating husbands being common, and had never even held a boy's hand myself.
I knew I was doing something bad, but I had been lectured about "bad" my entire life from an extremely religious father who was quite happy to crawl into my bed at night, and beat me black and blue in the days.
What I had with MM was the first bright ray of light I had ever felt, it felt like love, it felt like he cared about me, it felt like something in me was worth something and desirable. And the craving for that feeling totally and utterly eclipsed any half-baked notion of 'bad' I'd ever been taught.
Now (many years later, and much wiser), I see that affair for what it was. I regret what I did. I used my own pain to block out the fact that I was hurting someone else. I was stupid at first and genuinely believed him, and then I let denial sing to me because it sounded so much sweeter than the truth.
It ended when I met the wife (though she didn't know who I was), and I saw she was just a woman and not a monster. She seemed to me a better human being than he was, he was the monster, and I was something even worse.
I look back at myself then, and wonder only how it could have been different. How would I help stop another young person falling down exactly the same path?