Advice?

My partner and I have been fighting because I said I want to go to when our baby is a year old (she’s 6 months now) and he said that the thought of me doing that made him feel sick and insecure, I told him that I’m sorry that he feels that way and that if it makes him feel better I will get the equipment to do it at home, he has then said that it’s not about the gym and he thinks that I will be easily swayed to cheat on him (he had a history of cheating, I don’t and I could never cheat on someone) he says that it’s because I’ve said I’m not the same person anymore (I’ve said that because my body has changed, my mind set towards sex has changed I.e. I don’t really want sex much anymore, and that my focus has changed to be on our daughter who needs me more than anything) He has made me feel awful about wanting to do something for myself, I asked him would he feel insecure if I got more tattoos and he said yes… I’m not really sure where to go from here as this is just one of many arguments we’ve had