I think just cutting her off unilaterally is going to raise a HUGE stink and drive her into legal arms.
Is that what you want?
In my sitch, I found that I'm emotionally not ready to pull the legal separation trigger, divide the assets, etc. When I talked to the lawyer, I found that it is absolutely possible to make a financial agreement with my husband that gives me some security without doing anything too dramatic to the finances or the legal condition of the marriage. Owing to the developments in my sitch, I haven't done that yet either, but it's out there.
Like what your W has done or not, you are under certain moral and legal obligations to provide for your family. If you want to pull the rug out from under her in a way that keeps the road home paved, then I suggest you talk to a lawyer, find out what your legal requirement WRT support are, and then make a contract with your wife that puts that into effect.
Then, she can't ask you for financial help because she's getting what she's entitled to. She can ask you for other kinds of help, but as part of your distancing you can politely decline. But your a$$ is covered and she won't have recourse to the law that would force her to do more than you are willing to do.
If you do all that, and considering the conversation you had with her friend, then I think you should take a few weeks to think really hard about what it is you want.
My two cents.
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15
