Would you let your partner go to the gym with a femal coworker?

Me and my bf have been together for almost 2 years now. Im usually the jealous type, but i dont react on it and im usually able to talk some sense into myself. So my bf is an emt meaning he works 10 hours one on one with a coworker. Theres this one coworker he has thats a girl, and at first obviously i was jealous but then managed to tell myself shes just a coworker and that hes at work and this is how its going to be. Next thing i know he is telling me that she invited him to go to the gym with her, one on one. So at first i said okay, and i tried talking some sense to myself but idk i just had a really bad feeling. I let him go to the gym with his female friends in the past, because hes known them for a long time and i know them as well. But hes only known his partner for 3 or 4 shifts and i dont know her or her intentions.

To me its more of an audacity thing. I feel when i was single and i had male friends or male coworkers who were in relationships, i never tried hanging out with them one on one because I never wanted to cross a possible boundary in their relationship.

I expressed my discomfort to my bf to which he said "ok i wont go then", and i kind of feel guilty about it. Do you think im overreacting?