アバタもエクボ is a classic proverb, literally 'even pockmarks (look like) dimples' — equivalent to English 'love is blind': when you're smitten, every flaw looks cute. The speaker says they weren't united by a grand romance (大恋愛), so the 'love is blind' effect simply couldn't apply. ~わけではない is the standard soft-negation pattern 'it's not the case that X,' and ありえない ('impossible, unthinkable') is a fixed ichidan verb from 有り得る. の末に marks the endpoint of a process — 'at the end of / after'.