What, do आप think, was ultimately the downfall of Rhett and Scarlett's relationship? Pride....stubornness....vanity...?

For me it was blidness.
At Breakfast at Tiffany's होल्ली, होली कहा something like her greatest fear is not recognizing sometjing belongs to her until it's gone (I'm sorry I don't remember exact qote).

That's Scarlet's problem. She imagined she loved Ashley. She belived in it so deeply, that she wasn't able to recognize that
1) Ashley she admires isn't the real one, he's never existed. The real man is lost, damaged & pathetic- nobody she'd ever admire, प्यार या even like. Her प्यार was a projection of her mind and she was too blind to see it.
2) She was so busy with her imaginated प्यार to imaginated Ahley that she missed the fact that Rhett is the प्यार of her life: the one who supports her, protects her, understands & acceprt exactly who she is.She was taking his प्यार but she was to blind (& egocentric) to notice it.

Of course, Rhett's pride was a problem in this relationship. But I blame Scarlet more.She couldn't devide her dreams from reality. She was too blind to see what's going on in her life, what she needs & what she's दिया all the time... She was rejecting it साल after साल in the name of a childish कल्पना until she लॉस्ट it...

Scarlett always thinking she is in प्यार with another man. Scarlett loves Scarlett and loves to flirt