Put her things on teh front lawn and tell her she's not welcome in your home anymore.
Her friend is confusing "infatuation" with "happiness"... they are NOT the same thing.
It's not pursuing if you are just trying to educate her friend. But since those two are hanging out, she's clearly supporting the whole mess... so I don't think you will get very far on that route...
It WILL END eventually, a mess will result. It may take a few years, but it will END and she will regret what she's doing.
I would NEVER tell her I was out with someone else.. I would never have GONE OUT with someone else...
You are still married yes? Then SHOW IT... you just VALIDATED ALL OF HER BEHAVIOUR when you did that...
You are supposed to be setting an example for her AND for you...
Do NOT DATE until your divorce is FINAL.
You are in NO EMOTIONAL STATE to be getting involved with someone else right now anywyas... be considerate to OTHERS by not getting them involved in your life right now... they will just end up hurt.
You need to focus on showing an example here, for yourself to maintain your marraiges' integrity and to her friends and yours.
If you don't want to look desperate and crazy, then don't start acting like your wife and start cheating on her... that's NOT going to improve the sitauation... and...
If it was just a lie, then you still aren't helping anyone by announcing that.