What is my girlfriend slept with another guy while we were broken up?

I'm sorry to hear that your girlfriend slept with another guy while you were broken up. It can be difficult to process such information and may raise questions about your relationship moving forward. It's important to remember that during a break, both parties are free to do what they want, but it's also important to communicate and establish boundaries if you have certain expectations when it comes to fidelity. Depending on the circumstances, you may need to take time to reconsider the relationship and how you want to move forward. It may be helpful to talk to a trusted friend or counselor to gain perspective and process your feelings.