What does it mean that my girlfriend bought a couple's mobile phone case and bought other mobile phone cases?

According to the information you provided, my girlfriend bought a couple's mobile phone case and other mobile phone cases. This may mean that she wants to express the following possible meanings:

1. She wants to express her intimate relationship with you emotionally. Couples' mobile phone cases are usually a pair of mobile phone cases used together to express the intimate relationship and correlation between couples.

She wants to express her love and concern for you through the phone case. Buying a couple's mobile phone case is usually because she wants to show the relationship between you to the people around her, or to remind herself of her feelings for you.

She probably just likes the phone case. Some people like to collect mobile phone cases to show their personality and taste. So she probably just bought these phone cases because she liked them.

In either case, the best way is to ask her directly why she bought these mobile phone cases. This can better understand her intentions and thoughts. Remember, emotional communication is an important step in building a healthy relationship.