If you're worried that your girlfriend has feelings for someone else, the best thing to do is talk to her. Communication is key, and if you want to make the relationship work, it's important to be honest about how you feel. You can also try talking with a friend or family member who knows both of you well. They may have some advice on how to deal with this situation, or they might be able to mediate between the two of you in an attempt to make things easier on everyone. But if she’s decided to leave you, then there’s nothing to do but accept this painful decision, take space, and focus on your own healing.