Boyfriend use to like my best friend

I have a situatuion and idk what to do. My boyfriend and i have been together for a year we had broken up for a couple months and got back together. While we were broken up my best friend and him started hanging out a lot over spring break. He use to like her in HS but got over it. *btw i didnt know he use to like her until after we got back together* While they were hanging out he started catching those feelings back for her. But she declined cause she is my best friend and she has no interest. Since my bf and i got back together i been feeling he has been treating me strange when we are around her. Idk if its just jealousy or what. I just get really irritated when he makes her laugh or plays around with her cause he doesnt do that with me while we are all together. Am i crazy and this shouldnt bother me or what? Lol