What is why does his girlfriend stare at me?

There could be a variety of reasons why his girlfriend might be staring at you. Here are a few possibilities:

1. Curiosity: She might simply be curious about you, especially if she's heard about you or if you're someone new in her social circle.

2. Admiration: She could admire something about your appearance, style, or demeanor.

3. Jealousy or Insecurity: If she perceives you as a threat to her relationship, her staring might be a result of jealousy or insecurity.

4. Recognition: She might think she recognizes you from somewhere and is trying to place where she knows you from.

5. Non-Verbal Communication: Sometimes, people use eye contact as a form of non-verbal communication to convey interest, friendliness, or even confrontation.

6. Comparison: She might be comparing herself to you, which can be a common behavior, especially if she has any insecurities.

The best way to understand her intentions is through open communication. If you feel comfortable, you might consider talking to her directly to clear up any misunderstandings.