I was also thinking it could be used to justify a divorce, for infidelity on her part. However, that wouldn't be good since she doesn't want her kids knowing that...
In any case, Walt may have been wanting to do the right thing, but he really did isolate himself from his family as his priorities began to change, from actually spending time with them to doing something illegal in order to benefit them in the end. This distancing created a bridge between him and Skyler and eventually she just didn't feel a connection, as she realized the man she knew no longer existed, she just wanted to move on. Which is why she wanted to separate.
He didn't want to, and wanted the happy family he thought he had preserved;however, things change as did her feelings. I actually do think she has feelings for Ted, since they had hinted at them wanting each other for a long time. It was bound to happen, but this issue with Walt gave her the extra push, she really wants him out.
You can't pretend to be in "lala" land anymore Walt; this will probably cause him to start cooking though.
Willy105 said:
He did control it. He's back home with his family.
Skyler couldn't control it. And slept with another man.
This was more about their relationship already crumbling through his lies and deception than control, he put his priorities on money (for a good reason) but he didn't realize that it has destroyed his family.
Skyler wanted to move on, this is the only way she knew how.
It is most definitely a lose-lose situation, although she probably gets something she hasn't had from Walt in a long time. Either way, he has to realize he's lost her, and it's not going to go back no matter how much he pretends.