There is a person who always sends messages to my girlfriend.

Let her directly refuse or even sever contact with him. Since your girlfriend told you about it and asked your opinion, it shows that there is no ghost in her heart who cares about you and respects your opinion. As long as you say so, she will definitely do as you say. If that guy believes that your girlfriend will tell you again in the future, you can ask your girlfriend to warn her not to bother her again. If you repeat it, it's not your fault, even your best friend can't take care of it. Find someone to repair him or just ask your girlfriend to warn him of harassment. The most important thing is not to have any thoughts about it or make trouble with your girlfriend. The other party just wants to make trouble with you. He is waiting for an opportunity to take advantage of it. If you make trouble, the other party will be very happy. Besides, since your girlfriend told you that she didn't apologize to you, you should not only have trouble with her, but also take better care of her. It is not easy to find a girl who really cares about you. I wish you happiness forever.