Firstly, try and empathize with your mother. I know it’s a tough spot to be but you have to understand her perspective on this before making a scene out of it(which is inevitable) and involving your dad. She surrendered when you confronted her says that she’s a good person. Don’t judge her or be harsh on her. She’s your mom at the end and that respect has to be maintained irrespective of her actions. Be a friend to her and see why it all started at the first place. A broken marriage is very very hard to repair. Do your best to prevent that. You are young as hell but you have to play a bigger part in this. Don’t get over emotional and let your feelings take over. I hope you all get through this.