Bf wants to break up to lose weight

My bf said he needs to take a break from me, and he says the reason being because I’m making him “fat”. Mind you we have both gained weight being together for 4 years, not just him. He says that the last time he felt like “himself” was when we barely met and he was at “his peak”. He was a gym person, and he honestly did look good body wise, but hey, we both gained! That’s what happens in relationships sometimes. Idk if I should keep trying to convince him to stay, or let him be seeing how he’d rather leave me than stay with me and lose weight. (Which he says he can’t do)