Therapist says not to react but I think I might lose it at work

I've worked hard to get to ignore the ex-N and his consecutive OW at work. As the therapist has recommended, I've kept it brief whenever he engages me and done my best to avoid him in this ungodly situation of having to work together. She wants me to focus on being thankful I'm NOT the OW.

He is cheating on his GF with the current OW, and I can't stand having to witness it anymore. He is, for anyone with their eyes open, gallivanting around with the current fling. They went to Europe together a few months ago on "business." She is rude and surly with me, while he tries to maintain a very cordial relationship with me, sometimes for self-validation and sometimes just to irk the OW. Games are his forte and he acts like nothing ever went wrong between us. And this OW just keeps on taking whatever Mr. God-man dishes out.

I want to tell him to ***fuck off*** and stop speaking to me--or some version of that. He can't have all of his in his life, the cocky SOB. The therapist wouldn't advise that, I'm sure....

Things are much better when I don't have to be around them, but it's impossible in the workplace not to see/know it. I truly feel I'm losing my patience.