Bf playfully joked about my stutter and now I’m crying

Bf playfully joked about my stutter and now I’m crying I have a mild stutter. It comes out more often when I speak English since it’s not my first language. My boyfriend finds it cute when I make mistakes in English and we usually joke around that but never about my stutter. I’m tired, sleep deprived and working a lot which I swear makes my stutter even worse. We were joking about something and I stuttered and he proceeded to copy me and said I sounded cute. I guess he saw me upset because he immediately stopped but I just kinda smiled and went back to reading my book before I have to get ready for work. He left for school and as soon as he left the room I started to cry. We’ve been together for a long time and I’ve slowly gotten better with jokes because I used to take things so personal. He’s always understanding so I know if I tell him to not do that he will stop but I just felt hurt and uncomfortable and can’t shake it off. Update: we talked and he apologized, saying that he definitely came off as rude. I did admit I should have told him I was upset and he said I shouldn’t feel scared to tell him what upsets me. You guys were right, We just have to communicate but now we know. Thanks everyone for your comments!