How do I stop resenting my bf after miscarriage?

Hi all, I have been with my bf since January and got pregnant (unplanned) and had miscarriage at 12 weeks. Even though the pregnancy was unplanned and I was scared at the beginning I got bonded to that baby. My bf did not seem very emotional about the miscarriage and I even have a feel he was relieved. He did offer me all help I needed, hugged and spent time but I could tell he wasn’t upset about it. We work together and I would see him talking and joking with other coworkers like nothing happened while I was heartbroken about this situation. We have one pregnant coworker and I overheard him asking her how is her baby, how is she doing and etc., all happy. Honestly it was so painful. I broke up with him for a few months and eventually we got back together because overall he is a good guy but these emotions are coming back to me. How do I move on from this?