Good to see an update from you. It sounds like anger is something you could work on in IC, but I got to say that I think you're being put through some almost unbearable challenges. I can't even imagine going to a party with OW and dealing with her in the workplace like you have to. She clearly had not given up.
If you're not seeing an IC now, I think you could consider it. you need the support and a place to vent. I also think you could talk with a L who specializes in HR issues. It could be good for you to know about what could potentially be done about OW and her transgressions in the workplace.
I hope your holiday is peaceful and happy!
M 16 yrs, WH62, P54 3 adult blended kids EA 11/13, BD1 6/14 PA fall 14, BD2 2/15 Piecing 2015, BD3 12/15 Separated 4/16 WH moved OW in 5/16 Divorced 6/15/17