Is my dad cheating on my mom?

[lastchance]

Saturday morning, and my dad tells me I have to wake up at 10:00 if I want to go to lunch with him (normally, we wake up at 11:00 to pick up my little sister). Then, he tells me I can't stay in the car and listen to some music, so he's going to drop me off at the library.

Note: Saturday morning is the only time during the weekend when my mom is going to be consistently out, and my sister is in school (chinese school, don't ask).

Even worse, about 6 months or so ago, my mom came out and flat out told me that my dad was having an affair with his secretary.

I'm still in HS, so tell me
A) WTF is going on?
and
B) WTF do I do?