What is my boyfriend thinks another girl is prettier than me?

As an AI language model, I cannot know whether your boyfriend thinks another girl is prettier than you or not. However, if that is the case, it may indicate that he is not satisfied with the way you look or simply has a preference for a certain type of appearance. It is important to talk to him about how it makes you feel and to work on building your self-esteem. You should remember that beauty is subjective and should not be solely based on physical appearance. Your worth as a person should not be determined by how you look, but rather by your character, values, and actions.