My parents are getting a divorce?

My dad cheated on my mom and i knew for about a year before my mom did. she told my dad that she had known what he was doing for two months. she let him know this passed mothers day of 2011 and i don't know how to get over that fact that it is over between them. is it normal that i feel that i can't trust my dad. i am only eleven and i am staying with my grandma for one more month but i don't know what to do when i go back. What if i have to live with my dad i really do not want to live with my dad but if i live with either of them i will have to live in an apartment with my mom or with my dad somewhere in another school district and i really cant loose my friends right now. i cant get over this and my brother is leaving for basic training with the national guard. and im a teenage girl and all my freinds say im supposed to have fun but its just so hard