Posters on here will also tell of their predatory behaviour when they are divorced or widowed. The men become predatory and their partners often push the woman out of the group.
I know women who, while single, were constantly propositioned by married men; one while on holiday with his wife and kids. She thought she'd had a few friendly interactions with them; until he got her alone and announced he was coming to her room, after telling her she must be so lonely etc. She told him not to bother.
Other married men at work tried it on with her as well.
As someone said, some men see a single woman as an unused parking space - up for grabs. Others see them as lonely, desperate, and vulnerable. They think women feel the same way about sex as them and are desperate for it.
I don't think the majority of cheating men go after attached women ...or end up cheating with attached women; they aim for single women (through whatever circumstances).
A specimen I dated, who claimed to have good morals, let it slip.once that he didn't understand how single or attached men cheated with attached women ... Because they'd be shagging a woman who was also probably shagging another man; and that was unacceptable to him.