Aoo

It is fantasy, an immortal cannot be measured by human's time ¯_ಠ_ಠ_/¯
1. ML fell for her isn't her fault
2. ML did everything to not be seen as a child by her is smt out of her control
3. She saw the boy as love potential is the fruit of ML's labour and her accepting that the person she fell for isn't the kid in the past but the man in the present
4. Of course this kind of love isn't for normal human like us, it's for immortal in the land of magic. Asking for human morals in this set up is like ordering burger at pizza hut, simply doesn't make sense.
(｡☬０☬｡)

This type of behavior shouldn't be condoned but eh ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄ the fact that Daniel is sick made everything feels inevitable, Lion also use this to do calculated attack on other kingdom to benefit himself so it's not all blind love...
Imo, the only real downside is Rael's emotions felt kinda wasted ┑(￣Д ￣)┍