Addison Montgomery walks in on Meredith Grey cheating with her husband Derek Shepherd. She stays to help him finish the job (that he was doing inefficiently). Sex & Smut with Plot-Ish. Addek & MerDer to MerAdd & Mardek. Meddison. F/F. M/M. F.M. Meredith Grey/Addison Montgomery. How Derek Found Out. Crack. Fluff. Humor. Eventual Happy Romantic Ending. Rated E for Explicit. Twosomes? A Threesome- But Only Sort of... (Mostly Lesbian Content).