So she didn't just start an affair, she also didn't use protection... Even if she wasn't asking for a cream pie and the manager guy just did it without asking, it was her that should have enforced protection at all times.
And as for the cheating she's terrible no excuse. While clearly the duchebag husband is the person at fault in their relationship, cheating on him is not an acceptable situation. She should have filed for divorce. A loveless abusive marriage is not going to be good for her child in any way. "she was vulnerable, he said the right things, it's the manager's fault"... Just a big no, that doesn't detract from her responsibility. I would understand kissing him in the vulnerable moment, sure. Then think of what she did and either do the right thing or fall in the dark hole. But this slut proceeded with getting in all fours, getting fucked without protection and then cream pied leading to this. Wtf did she expect?
All 3 of them are terrible ppl in this situation but her decisions are dooming the life of 2 children.