So sorry you've had to join our lovely club....
You have kids in your house, correct? Her seeing someone else right now is not in their best interest. Put her crap in hefty bags and tell her to go move in with her new AP. He should be happy to have her stay with him, right? Because he's probably not married (sarcasm).
Then change the locks. You're still married and there isn't room for a third person in the marriage and it's not healthy for your kids to witness this. Focus on you and your kids and get her out of the house now.
For the anxiety, you may want to get yourself to an IC and get meds. I had to and it has helped a ton. Until then, you can try GABA or Calms Forte. They can both be found in health stores. Calms is sold at most pharmacys in the sleep aid section but it works for anxiety too.