How would you cope

So my SO cheated on me as I found out earlier this year in February..they slept together etc, I took him back, we also have a little boy together..I don't fully trust him yet as that will take time of course. Tonight he is out on a works thing, she works with him..she will be there.

He only has contact with her at work, because he has too. No messages no calls from her or from him since i called him out..but I can't help but feel irritated, upset and really fucking pissed that he is there tonight..and by the looks of videos posted on facebook he was allocated for the show next to her. I hate the fact that he works with her and has to see her every day, it sounds dramatic but it makes me so frustrated knowing he knows what she looks like under her clothes, how she is in bed etc..the connection was there before between them..what if it rekindles tonight..I've been on a debby downer all day..he promised nothing will happen..the show has finished now and he is in the bar but no doubt with her and maybe 2 other people..I hate the fact that he is even looking at her or even conversating with her..I am basically ranting..I need to get it off my chest. I'm not interested in any "if you don't trust him get rid" comments..normally everything is fine but I just hate today..maybe im selfish? My head is in bits, I can't sleep..I'm half minded to go and just rip her head off anyway for even breathing near him, the other half just wants to dwell in my own pity.