boyfriend is shy to shop bras with me

i told my bf i needed a new push up cause the one i wear is getting tight cause my titties keep growing and he was like "okayy but i aint going in with you" 🙄 I was likeee what's the difference between going up to the cash with me with a pack of period pad and going in a store to shop bras and undies with me??? i just don't understand lol excuse me in advance if I'm wrong for feeling this way😪 I mean yeah it's full of women but I've seen so many times, guys with their gf in lingerie store shopping together looking normal and stuff