Yesterday...

It was a great birthday at first but then my grandma pulled me aside and said that my mom is being cheated on (which I figured because I’ve seen his phone) and explained the situation to me. Tbh I wish she’d let me learn from my mother because she seemed fine and didn’t want/need to talk about anything.... She said she isn’t leaving him and I don’t know what to do about it. I don’t want her to feel the same kind of heartbreak that she did with my dad. What should I do??