The "I'm through with you" card is the actions she sees from you. Words will mean nothing. Remember, her lips are moving, she's lying, so words mean very little to her. Telling her that is actually counterproductive.
Speak softly. Your big stick is the actions you show her.
After reading your sitch, I see you continuing to enable her behavior by using the excuse your texts and calls concern your S. He's doing fine. I don't call the EX-WW kid related things unless they're in the ER. All other things I can handle. If a question concerning dates and events with the kids comes up, I text. I have texted the EX-WW 3-4 times in a week. That is all I have to do.
I did have to set the boundary to her that I no longer wished to be her friend, so no more texts, emails, showing up at work, etc. Personal emails or texts only. I even told her not to call! I want nothing to do with her as she starts her new 'happy' life with OM. She burned the marriage down to the ground, blamed me (of which my addiction played a big role), and continues to do so. I don't need that guilt in my life - she's blame shifting. It sounds like yours has done the same.
Keep focusing on yourself and your S. Being completely dark to her is your new goal. Will you feel like a jerk at times? Certainly, it sounds like you both had co-dependancy. But, you need to strengthen your wings. It's called growth. It's really hard.
My best advice on this board came when 2 X 4's came to my forehead. I appreciate those hits more now after the D than when I was in the middle of it. I'm not being very soft in my words - so you might not like what I have to say. I know I'm speaking the truth in love right now, so I hope you understand. Keep up the fight.
M46, EXWW46 M15 T17 D20, S19, D13 M - Addiction since 1998 W EA/PA #1 2013/2014 W EA #2 June 2015... BD 1 Big D talk 9/15 BD 2 - EA/PA disc 10/30/15 Served D 1/22/16 Divorced 5/25/16 (yes, that fast!)