The point of the the Beauty and the Beast comparison is that his true self is being concealed and she eventually sees through to it when no one else does. She has seen him at his absolute worst, in the worst moment of his life (killing Han) and she knows his darkest, ugliest emotions intimately from being in his head, but she learns there is so much more to him than that and that he is in need of help and compassion.
Whether the Beast is a completely innocent victim cursed because of the sins of his parents, because of the whims of a faery, or because he was selfish (Disney version), all versions are about Beauty's ability to see the truth which others don't and to love him for his good heart in spite of his monstrous appearance. To love him stripped of all artifice (he also loses his ‘wits’ and charm in some versions of the curse) out of pure soul-to-soul compassion and connection.
This is the fucking plot of TLJ. It is entirely built on their emotional kinship (which was established in TFA) and mutual compassion for each other, they fall in love with their most naked inner selves, with respect and total honesty. What stands between them is a failure in that honesty when their courage is tested, a breakdown in their open communication: false beliefs, fears, and defence mechanisms reassert themselves. They didn't get all they way there because the story was cut off right after the turning point where the real obstacle is revealed and then it was subsequently ruined by morons, but the bones of it are there.
His transformation isn't about erasing his flaws or making him into someone else, it's about revealing the person he has always been and rewarding him with the freedom to live as himself. To live without constant pain and terror, to be able to reach out and love the way he’s always desperately desired; not to have claws and fangs you can’t control, not to be an animal lashing out in fear, to be a man. Redemption is healing and healing IS possible. It doesn't mean you are perfect now and will never make another mistake, it means you have forgiven and accepted yourself as you are, you will have compassion towards yourself and this forgiveness will allow you to participate and contribute to the world instead of shutting yourself off from others in fear of both hurting and being hurt.
(Which is why exile is failure in SW and why a huge part of Luke’s arc in TLJ is about how his worst mistake wasn’t the moment of weakness where he almost succumbed to dark side fatalism, it was his refusal to forgive his own weakness which resulted in the misguided attempt to punish himself and thus abandon Ben to Snoke and the galaxy to its fate. Human frailty doesn’t have to result in catastrophe, giving up and abdicating your responsibilities AKA being selfish results in catastrophe.)
Rey knows exactly who he is, she saw the monster and the lonely boy and everything in between, she isn't looking back to some idealised version of him. She wants to free him because she understands that he's a victim, but she doesn't drag him kicking and screaming because she also knows it's his choice and he has agency.
Her failure was in not knowing herself and her unwillingness to be vulnerable except as an absolute last resort, to admit that she wants him and needs him, that it isn’t all about The Cause. (Rey needs him because he is the only one with whom she can be or ever is vulnerable and honest.) She goes for the lightsabre and communication ceases. The throne room scene started going south in the first place because Ben didn't have the confidence or belief in his own value to offer her simply himself instead of a kingdom and because Rey didn't have the courage yet to offer him her unconditional love. She loves him and her love is not conditional, but she didn't give him that. She doesn’t tell him that. Both of them are still too afraid in that moment to actually lay things out.
Ben doesn’t understand that Rey isn’t rejecting him or saying he isn’t enough for her or that he’s doomed or any of the other things he’s perceived as the cause of betrayals and his broken relationships (he makes everything his fault- hence his self-loathing and fatalism), she’s rejecting his worldview. And Rey doesn’t, I don’t think, understand what exactly is preventing him from coming with her or turning away from the FO and that it is the fear which sustains the toxic worldview. This fear and Ben’s fear-motivated selfish choices are ultimately what is separating them. Acceptance always seems conditional to him, he’s convinced he can’t meet the conditions, so he spurns the ‘offers’ rather than face another failure. This is baffling behaviour from the outside.
They love each other and they’re heartbroken that it seems lop-sided, that something ‘empty’ (power, the Resistance) appears to come first; they feel abandoned again. There’s both a misunderstanding and a genuinely enormous obstacle between them, but they still love each other: that’s the set-up which makes their separation and place on opposite sides so dramatic.
The B&tB analogue has Beauty denying that her love is romantic and returning home to her father (and sisters, depending) and her childhood. The Beast will die of heartbreak (or the rose will run out of petals) if she doesn’t face adulthood and admit what she wants and return to save him. Ben has been a heartbeat away from coming home ever since Han’s sacrifice shattered his illusions, but he needs to be shown there is a home for him to come back to and that his life has value. That love is not transactional.
