My girlfriend's breasts are too small, and I'm too embarrassed to tell her. What should I do?

There is nothing we can do about it. In other words, it's no use telling your girlfriend or not, and it's impossible to make her breasts bigger, so there's no need to say it. There is no point in increasing her unhappiness. If you can't accept her airport, then break up. If it's acceptable, be tolerant.