You've heard me say, Borderlines see marriage as an End Game. They're silly enough to think, if he's willing to MARRY me, he must really LOVE me, and I don't have to try so hard anymore! This is unfinished business with their maternal attachment, and never having felt truly cherished and adored.
I don't know about You, but if I'm not feeling someone's adoration and devotion, I sure as fuck don't wanna pledge the rest of my life to 'em (or even, another few months!).