Is this a stupid thing to consider breaking up over?

my boyfriend has a history of being critical of the way I look which I talked to him about and he’s improved on, it’s been a while and I still can’t get over this one comment he made, I was feeling really confident in what I was wearing I naturally have the second smallest cup size, I normally wear padded bras but I went out bra less with nipple covers in a cute top and he looked at me and said you look flat. I just don’t get why the hell any guy would think that’s an okay thing to say?
Is this a stupid thing to consider breaking up over?
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