It's been a while since I've watched, too, but I remember this part because most people misunderstood her motives for cheating, and I've had to explain it before. Walter had shown her, at this point, how awful he was and he had also made it clear that she was stuck with him, doing whatever he wanted, whenever he wanted, and that he wouldn't leave and she couldn't leave. She was trapped with him. The cheating was a chess-move, a deliberate choice to make him leave, because it was the only way she could make him.

So I’m disagreeing with you here. I think she has reason to believe that her husband is cheating on her at that point and that while not ok behavior, listen she starts the series as stressed as she probably thinks she possibly can get, and then as her husband gets meaner, starts treating their kid worse and in some cases abusively (forcing him to drink alcohol), and then starts behaving in textbook cheater fashion. She snaps and cheats with her boss who shows her kindness and desire. I get it. It’s not good, but if a male protagonist behaved that way he’d be seen as complicated.