I believe that's true. That's how it happens. I know because I was in a relationsip for a long time with someone like that. However in the case of TM and having an affair there is an added issue to me - i can understand her falling in love with him and not realising what he was like. But she knew he was married and that's that, it doesn't matter what else is in play - he was married, therefore out of bounds if you have any strength of character and concern for others. And I have been in the situation of falling in love with a married man. I avoided an affair because he was married. It was hard but I managed it. We eventually did get together for a short period when he told me he had ended his marriage, but he was not totally honest about that (they were still living in the same house) and when he resumed things with his wife we both ended it.
I'm not saying I'm some sort of saint, just saying I have no sympathy for Toni McHugh. She is a selfish woman. She contributed to pain for another person, she is an adult, and she doesn't have to have everything she wants.