How to handle seeing my ex with the girl he cheated on me with?

I was seeing a guy for a few months, not long, but enough for me to get pretty attached. He ended up cheating on me with a younger, prettier girl. He and she both work in the same industry as me so I have to see them together regularly as he brings her to almost all of our industry's events. I can usually avoid crossing paths with them but he tends to bring her to eat meals with my team.

I have long since gotten over him at this point and even have a new partner I just celebrated 1 year with, but seeing my ex and his girlfriend together still brings up tons of insecurities even after all this time: wondering why I wasn't good enough for him, feeling like she is a better version of me (she also seems very sweet and good at her job. My team likes her a lot. And I don't think she is aware of the cheating and I don't intend to tell her). Feeling the hurt from being used by him all over again and pathetic that I let him treat me that way. Seeing how much more committed he is to her than he ever was to me.

How do I handle this gracefully? How can I cope with this? Why am I still struggling with this so much even over a year later? I seriously just start spiraling when I run into them and it affects my work sometimes. This is my dream job so I can't quit because of this. And he is not going anywhere any time soon either.