Is my dad cheating on my mom? (xposted to OOT, yeah, i'm a moron)

[lastchance]

My parents have had a lousy marriage for a long time, and I guess it didn't really surprise me that much, considering how emotional my mom gets (I probably subconsciously knew for a while).

Friday Night, and my dad tells me I have to wake up at 10:00 if I want to go to lunch with him on saturday morning(normally, we wake up at 11:00 to pick up my little sister). When I ask him if I can stay in the car and listen to the radio, he tells me I can't, 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 right now?
and
B) WTF do I do?