I broke up with my girlfriend, but I sent her a message because I couldn't let go. Then she called me back and said, in what capacity should I talk to her?

According to your question, you broke up with your girlfriend and both of them are single again. You sent her a message again, caring about her only because you couldn't let go, and it had nothing to do with your girlfriend, but you bothered her because of your ex-boyfriend. Since we chose to break up at the beginning, we should take the initiative to face the practical problems after breaking up. You are no longer a child, and you can't make decisions according to your own preferences. The sign of maturity of an adult begins with the courage to take responsibility. There is still a long way to go in one's life. When this road comes, new things will happen, to meet new people and experience a new life. Maybe one day these new people will become old people again, but this is life after all, and imperfection is the norm.