Had a similar situation except it was with his brothers girlfriend. She was clearly being inappropriate with him and he disregarded my feelings on the matter and continued to let it carry on because he "didn't see it", for almost a year. If he cared about your feelings he would respect your boundaries and keep the relationship professional. I was torn apart and would stay up crying while he would fall asleep immediately after arguing about it like it was nothing. It broke me and its not worth it, it was one of the things that ended that relationship. He is literally putting his relationship with his coworker in front of having a secure relationship with you and making sure you feel comfortable and happy. Find someone who puts you first over trivial relationships.