Daisy cries when Gatsby shows her his collection of tailor-made shirts because she knows it is vulgar to be showing her the shirts in the first place and bragging about how he has them specially made and imported. The shirts themselves are in bad taste because they are too colorful and ostentatious. Furthermore, Daisy cries because she understands that Gatsby doesn't even realize he is being vulgar. She understands that he is trying to impress her with his wardrobe and is doing just the opposite. She may have been infatuated with him once when he was a handsome young officer, but she cannot love the man he has become. She is crying for herself and for him and for the cruelty of life and the remorselessness of the passage of time. She probably feels that she does not deserve the worship that made Gatsby spend so much of his life trying to become worthy of her.
daisy wouldnt marry gatsby originally because he was not of the same social standing as her and he didnt have anything to offer her (financially) but she loved him all the same. At this time women were almost second class citezins even though they were becoming more free daisy loved gatsby but she had to marry tom to be financially stable. when she reunites with gatsby and she sees he has all the money and cars and indeed shirts and he is so boastful of them she thinks he is not the person she fell in love with
hope that helps :)