Innocence Lost

Why does everything pure in Gareki's life always have to become tainted or lost? Or at least that's the way it always seemed before he met Nai. But there was someone else long ago, wasn't there? Full Summary Inside. Spoilers for Anime & Manga Alike. A/U (How Gareki and Yogi first met). This story is rated M for… reasons, nothing sexual will be shown (though it may be hinted)...