You aren’t the one who is in danger of ruining your family. Your parents are. Hurting yourself isn’t going to solve anything. I do understand that saying that you might is a way to tell us how awful you feel. I get that you love your family very, very much.
Your parents have a marriage problem to solve. The life of a trucker and spouse is really, really hard. Often it’s lonely. Your mom may be interested in someone else but your dad probably also has some part in their growing apart. This is their problem, not yours. They both will always be your parents. They can love you and your brother and be there for you whether or not they can find a way to renew their love for each other. None of it is your fault or your responsibility. You and your brother are the kids in the situation. It’s time for the adults to act like adults and deal.
What you do now is have a serious talk with your mom. You’ve been close so I’m guessing you know how to approach her. Let her know that she left a trail on Facebook and that finding it has been very, very upsetting to you. Tell her that you understand that her relationship with your dad isn’t your business but that you want very much for her and your dad to figure out how to stay together if they can. Also tell her that keeping her secret is too heavy a load for a 13-year-old boy. You love her and you love your dad. It’s unfair for you to be caught in the middle.
If she doesn’t listen to you, think about whether there is a relative or someone close to your family who you can confide in and who you can ask for help. If that isn’t possible, do consider asking your school guidance counselor for support in talking to your mom.
I’m terribly sorry that you are suffering like this. Turning the problem back to where it belongs – with your folks – won’t solve it. But is will relieve you of some of the strain.
I wish you well.