I feel like giving Tenna to Mettaton isn't exactly the great heroic move it's made out to be.
Tenna has spent his whole life serving Lightners, he loved the Dreamurrs and cared deeply about them, but they never loved him as a person.
They never viewed him as a person.
To the Dreamurrs he's just their TV, an object. As a Darkner of course he loves to be their TV, it's Darkners' purpose to serve Lightners. But loving a higher power that doesn't even view you as a person isn't love, it's worship.
"Worship isn't love. It's distance, dressed as devotion. You can't hold someone from a pedestal."
Every Darkner we meet, we bring back to Castle town. Because in Castle town they're not just possessions, they're people.
Darkners in Castle town aren't living for a higher power that doesn't view them as a person, they're living with people who are equals, people who view them as people. The Darkners we bring back to Castle town are living for themselves for once, and the people who care about them don't need to be The Almighty Lightners, because they actually care about eachother as friends and equals.
He wants to be wanted, he wants to be wanted by Lightners. He has lived his whole life based on the idea that the only thing that matters is being loved by the Lightners, that the only thing that matters are the Lightners, and it's not easy for him to just let that go. He's so focused on being cherished as a Lightner's object that he doesn't even see that people like Susie actually care about him as a person.
He feels lonely in Castle town, but giving him to Mettaton just doesn't feel like the right thing to do. It's giving into his idea that the only thing that matters is being a Lightner's object.
Mettaton is thrilled to have Tenna, to have entertainment. But Mettaton doesn't know about the dark world, he doesn't view Tenna as a person.
Tenna struggles with letting go of the past, he holds onto the memory of being watched by Lightners and he wants to get that feeling back. He doesn't want to move on from being a Lightner's object, he just can't fathom the idea of living for himself.
Giving him to Mettaton is the quick fix, the short term happiness as opposed to a long term solution. It's the Dreamurrs all over again. What happens when Mettaton eventually discards him like the Dreamurrs did? Will he just find a new Lightner to worship? How long will he chase the idea of trying to recreate the past of being someone's TV?
Isn't it better to live for yourself, than to worship someone else who doesn't even see you as a person?
I feel like in Castle town, he can learn to live for himself, he can learn to see that the people around him actually care about him as a person, and that he's loved for being himself.
Sure, it's not easy to move on from trying to impress people who don't see you and to realize that people care about you. Of course he will feel sad and lonely, healing and recovery and moving on isn't all sunshines and rainbows, but I truly think that he can find a real happiness with people who care about him.
It gives me hope that even though the road forward is messy and gloomy, that what lies ahead is worth every step, and that someday looking back at how far you've come will feel like you can take on whatever's next, and continue moving.