i just wanted 2 say i am in exactly the same position, and i think my dad is having an affair too.
i have friends who's parents have split up, and being with them has made me realise that u can still cope if ur parents split up, and i know it sounds cheesy, but they will both still love u.
if you've thought about it as much as i have, u will eventually realise this.
don't worry; your life will still go on.
this probably hasn't helped, i just wanted u 2 know that ur not alone