if this is a genuine question, then you should understand that breasts come in all shapes and sizes, and the firm orb-like ones you see in the media are rare on a woman over 19 unless surgically enhanced. Your girlfriend obviously feels comfortable with her body, and she is absolutely right to feel this way. You must be extremely careful not to knock her confidence, because this is a problem you have, not her. Ask yourself why you are feeling like this, what are the real issues. If you were happy for her to go topless before, then are you treating your girlfriemd as some sort of trophy to be paraded around? Some men do not like their female partners to go topless, and they may have valid reasons for this which they can discuss as a couple, and reach a decision both partners are happy with. Yours does not sound like a valid reason to me, you have come across as immature and shallow, and if you approach your girlfriend in the same manner, she will be hurt and upset.