Start Again

AU: What if Derek and Addison didn't end things after Derek cheated on her with Meredith? What if they decided to give their relationship one more shot? Takes place after Derek and Meredith have sex in the exam room in 2x27 (the prom episode). In this AU, Derek already knows that Addison and Mark were more than just a one-night stand (even though I know that Derek doesn't find out