This situation more over connects to the emotional phase where a person feels the pain mentally and shortly loses his senses to understand the difference between right and wrong. In your situation, something similar might be happening to you. Here, you have two ways you can handle the situation:
 
End your relationship:
This might be your prior thought at first that you might want to do. This should be your decision on how you want to react to your situation, if you feel you’re with a toxic person then you must get rid of this relationship as mental health matters a lot and no one should be free enough to affect that. This is one of the ways you can think of. You must be mature enough to understand what happened and how you should react towards it. 
 
Will communication solve the problem?
Yes, there might be chances that communicating with your girlfriend can solve this situation. As you’ve mentioned above if you love your girlfriend and don’t want to leave her then you can try communicating with her and let her explain why she did what she did. You might give her a chance if you strongly feel that things will change in future. But, before that, you must be prepared for all the aspects and consequences that might come in the future. 
There are lesser chances that you can get any legal support in this matter, although there should be a lawsuit for cheating on your partner even if you’re not married as emotions matter and mental health gets destroyed too. You must be aware of the consequences you might face with time being in a relationship.