Welcome aBoard, Cath. Your book sounds great. Well, there's always 'old flame'. First love or first crush, if the number's correct. (Somehow second love, etc., just doesn't have the same impact!) Oh--heartthrob? I suppose you could get lengthier with something along the lines of "the one whose protective shell remained impervious to the love I poured over it" (yeah, yeah, sign me up for Bulwer-Lytton). Or how about "mistaken soulmate"? Also--you might try a thesaurus, if you haven't.