Do I only have sex with a girl named Zhang?

Maybe this is your subconscious mind at work! Because your first girlfriend's surname is Zhang, it may happen that the second one is also Zhang, so subconsciously, you will pay more attention to the girl named Zhang. It is also because of concern that there will be a next girlfriend named Zhang. In fact, regardless of these, Zhang is not a surname in China after all. It's normal to meet the same surname! Maybe open your heart and pay more attention to the girls around you. Maybe you will find that there are many good girls with other surnames, not just Zhang! I wish you happiness!