Based on what I read from H's threads, it is a difficult transition from their role as provider and protector of their W into a more isolated or independent position. What I'm saying is that while she has chosen to leave her family and her marriage, she freely removed herself from the umbrella of your protection and provision. She fired you as her H.
The best thing you can do for your stitch is to cut off any and all finances that are not court ordered for your WW. This is not encouragement to show vindictiveness, but to protect you and the children, and to hopefully cause her to see what she's done to herself. It is not your job to worry how she'll make it without your support. Unfortunatly, the WW who bombed her family, often has to deal with harsh reality before their fantasy world begins to crumble. When you were giving her $900 a month, that enabled her to continue staying in with the biker.
What you always considered as your responsibility toward your W will need to take a back seat so that you can rationalize from a different perspective. The heart of a wayward is extremely selfish. Yes, she feels entitled! It will get worse, so be prepared.
I have a thread about wayward wives, I encourage you to read it. Your W sounds as if she fits the bill.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!