Well, he knows how in love his parents are so no hope while Prime Minister is alive. And if he had doubts before he certainly knows now that his step mom has it bad for older men. So he'll bide his time and by the time his dad passes away he should be closer to her ideal type. It's a forbidden crush that fits with a villainous family.
That said I like to think that he's just young and Celeste was the first woman who seemed genuine towards him and his father. And that he will eventually find someone else using his stepmother as his standard.
He obvi has some insecurities about the physical defects of his father enough to go out of his way to be the opposite. So Celeste being gorgeous and addoring her classicly unnatractive husbands made an impact on him. Also she very clearly saw him and his father as two very diff individuals physically which was a relief for the son.
Yes! Exactly! (๑•ㅂ•)و✧
Welp, ngl, that ending was pretty hot in a forbidden love sort of way hahaha at least he aint aiming for her while the dad's alive. Just aiming for the future instead lol