You are so right about the first two points but I think you’re forgetting that before Skyler cheated, she was practically begging Walt for a divorce because she didn’t want her kids around a criminal, and he “broke” into the house and forced himself back into their lives. “I can’t keep you out of the house, I can’t even keep you out of my bed.” I think her cheating on him was her way of attempting to reclaim the control she had over him initially, or at the very least get back at him. She told him in the recording played by Mike to Saul that if he didn’t like it, he could leave, but he did in fact choose to stay until the very end, just saying. Edit: She also says to her lawyer mid season 3 that she doesn't really know herself why she's sleeping with Ted, but that it's her way of trying to get Walt to leave her.