In the spirit of DBing, maybe you can suggest that if she feels the need to leave the kids by themselves to go out, that she calls you and either you go babysit or have her bring them to you before she goes out. No expectations, no strings.
She is not thinking rationally right now and you cannot expect her to. She is apparently confused about her life and where she fits in as the mother of her children. She is trying to find her way. She must do this by herself with little or no help from you.
Regarding wanting your S back. I understand why you want her back. She is your W, the one you chose to spend the rest of your life with. However, the person she is right now is not your W. She is a confused woman who is trying to figure out what she wants.
I have no doubt that she loves your children 100%. She is just not herself right now. That is why you need to protect the kids. She may not be capable of that herself right now.
As far as this being your fault!? You need to let that one go. It takes two to make a marriage go bad. She is just as much as fault as you are. She just cant see that because of all the emotions and feelings she is experiencing right now. You should empathize with those feelings she is experiencing. She cant help feeling the way she does. Those feelings are very strong and you can not fix them. She must do it herself.
Take care of the kids and GAL for yourself. Detach!!! The kids come first over everything! You are their father. Your obligation right now is to protect them and if she doesnt like it, thats too bad. She will eventually see that you are acting in the best interest of your kids. She will respect you for this even though she will probably never admit it to you.
