How tf
He's been acting like a child/pet the whole time.
Even his mental iq fell when he became a bird.
He is mentally and physically weaker than he used to be which results in him acting childish.
Their whole dynamic is MC being the Duke's pet.
Mc is relying on food, shelter water, protection from the Duke and only knows how to act cute and help in a limited way. He gets an almost unconditional love from ML from the start, like a child or pet does. Ml looks at him on more of a small cute companion rather than a life partner.
He can't even walk properly now, and has to be carried and trained to walk ( like a person does to their kid). It is not helping that the Duke is ages older as well.
I honestly root for the Duke and the original lover to be together.
But the author do have a lot of character development to get through if she wants to justify them being together
I cant see MC as anything but ML's CHILD