Bf doesn’t want me going to gym with him..

My bf wants to start going to the gym again and mentioned that he’s gonna sign up and I said that’s good.. I wanna start going too and he looked at me and got mad and said “I’m not working out with somebody who works out like a retard” and I honestly thought he was joking and I said “I don’t know how to work out” and “you can’t show me?” and he straight up said no.. so I asked why it was a big deal and that it just goes to show how good of a boyfriend he is for saying all this shit.. then he goes off and starts calling me names (retarded bitch, stupid bitch, ect). We’ve been together 5 years almost and live together 4 years now. The funny thing is.. I didn’t even ask to go with him I just said I wanted to start going too. I honestly can’t believe he just said all these things to me. I’m in tears.

UPDATE: also let me add that he also told me a second ago that if I go all he wants me doing is cardio and I don’t think he’s wanting to work out alone because he told me when we first got together that he always taught girls how to work out.. who went to high school with him. I’m breaking up with him tomorrow. I am just completely stunned by the way he talked to me tonight and tbh I feel like our relationship has drifted. I’ve let him get away with so much including cheating in the beginning of our relationship (5 years ago) so it may be a possibility that’s he’s cheating again which is why he’s getting so defensive about the subject.