It's a big surprise and shock. I say confront your mom. It's up to her to address these things with your father.
You might want to find someone to address all the disappointments with that isn't your parents.

I know it's a sense of betrayal I've lived that feeling myself about my own parents. Eventually, years down the road I came to understand and truly see how my father can build his own walls and push away and not truly listen and actually got how my mom would have begun an emotional affair with a family friend. And my dad eventually left his second wife for another woman. Which turned out to be an important piece of that puzzle of why my mom did what she did.