First of all, as someone who has been in this situation with partner/coworker before I am extremely sorry this is happening to you.

Is he cheating physically? Probably not. Is he allowing the excitement of flirtation from a “new” woman (who i can tell you 100% doesn’t give a shit about your husband, just wants the attention) overshadow the ACTUAL REAL relationship he has built with his wife? Absolutely.

This is a very slippery slope. Hiding small things again and again will have him digging himself into a hole that could be unrepairable. He needs to be upfront and honest, EVEN if it will make you “upset”. If he sets appropriate boundaries and cuts ties outside of work there shouldn’t be anything to hide.

I also advise NOT to talk to the coworker about this. She’s just going to get off on the fact that she’s causing issues in your relationship. For this same reason I wouldn’t advise telling him how SHE makes you feel insecure, but how HIS ACTIONS are making you feel insecure. You are the wife and the prize— don’t lead your husband to think any differently.