I am so sorry to hear about the difficulty in your parents’ marriage. Try to remember that while they are your parents, these are adult situations in a marriage that you are not a member of. As upset and betrayed as you must feel, it is not your responsibility to work out your parents’ marital issues.
Secondly, being angry is okay. Your life is being turned upside down. You love your dad, you’re outraged that your mother acted against her marriage vows and hurt your father, your stability, the family’s security and happiness. Please give these feelings a voice and do NOT try to bury them out of fear.
How to speak to your mom now? I would say, with honesty. As difficult as it might be for both of you, I would calmly and charitably tell her how this makes YOU feel. I would not speak for your father, though it is perfectly acceptable to say, “and it hurts me because I see what this is doing to dad.” But I would definitely tell her in as many words as you can, that this hurts YOU, that you don’t agree with it, that you’re surprised and utterly disappointed. That you’re afraid this will change how you feel about her and what sort of relationship you’ll be able to have with her at this time or even in the future.
Thirdly, yes, this can be forgiven. Both by God and by you. Pray for God’s mercy on your mother’s soul, pray that she sees the error of her ways and returns to your father’s arms. Pray that you can act lovingly toward both of your parents. Pray that God can put a spirit of forgiveness into your heart. Pray for a willingness to return to the sacraments–for all three of you.
Also, I would ask my parents if I could see a Catholic counselor to process some of these feelings and the panic you must be feeling. Check out CatholicTherapists.com to see if you have counselors in your area. Even if none are listed in your state or city, you can contact your diocese Family Life office OR Catholic Charities and they can refer you to a Catholic therapist. If you are uncomfortable doing that, I would speak to either my parish priest (do not worry about the fact you haven’t been going to Church, he is there to comfort all members of his flock) or my school counselor.
Yes, I would return to the sacraments. Go, first, and receive reconciliation with God. Check out your parish’s bulletin or call the parish office to see when confessions are offered in your parish. Let His mercy wash over you. Go, too, to mass and receive our Lord in holy communion. He is waiting for you! Turn to him when your heart is so broken and needing repair. He loves you.
I will pray for you.