my boyfriend thinks im fat...what should i do?

ok so i got a new job and my uniforms are a little bit too small, when i told my boyfriend about it he said you need to lose weight, when i asked him what he was talking about he said that i have gained weight and i need to lose it, he wasnt saying it in an concerning way or anything. he literally just thinks im fat. hes apoligised like a thousand times for saying it, but how am i suppose to feel good around him now i know he thinks that about me?