This place is so weird sometimes! So many posters falling over themselves to defend your partners clumsy comment.
There was no need to point out your size/weight at all. You told him you’re joining a gym. He could safely assume it was to improve your fitness. He could have asked which one, does it have a pool, how often are you thinking of going, any particular classes you fancy etc.
instead he asks “because you’re heavy?”
I’d be pissed off too. In fact its exactly the sort of thing my DP would say/has said and its a jolt when the one you love casually calls you fat in a conversation, even if its one about health!
Of course fat people know we’re fat, we have eyes and mirrors and scales and clothes. Some of us just kind of wish our partners didn’t see us as ‘the fat one’ or mention it so casually as fact.
And re the nose comment, if my friend or loved one said they were getting a nose job, I would NOT say “because your nose is big?” I’d say “aww I love your nose, it suits your face, but I guess if it will make you feel happy and more confident you go for it.”