You see I don't believe he was disinterested in hoyeon. More so just disappointed about his looks? I'm pretty sure he loved hoyeon regardless. The thing with his child in the past. He never liked the kid's mother anyway and when the child was born it came out looking like him. It prolly saddened him to think that his child couldn't be a mixture of him and hosik. Which is why he showed disinterest in him. Not only did the child look like him. It also didn't share hosik's blood. But hoyeon was a different story even tho to him the child didn't look like hosik. It still came from hosik the person he loves the most so he accepted him.
Btw I agree with your theory. I just don't agree with the disinterested part. Disappointed yes. Personally I don't think sunbae could be disinterested in anything hosik haha. But I do believe his past self was disinterested in his child for sure. Personally I think he would have been more accepting if the child just didn't look like him at all
I think I forgot to mention "disinterested at first" cuz he obviously loves hoyeon a lot now
Oof
I have a theory could Sungyeon's disinterest in hoyeon when he was just born be due to his past life when he didn't really care about his child at all. I mean he legit got dissapointed that hoyeon didn't look exactly like hosik. Also it is said that sungyeon had low sperm count but still got hosik pregnant twice could that be some sorta "blessing" for them to be together after failing to do so in their past life? It's like everything is set up for them to be together without any obstacles with supportive parents and everything. It really does makes sense. I really love this story and cried like a bitch at the ending. It gave such bittersweet feelings. I hope we get to see hoyeon and soyeon all grown up one day T0T