I wouldn’t consider this a BL, it’s more of two strangers enjoying each others company and five novelist just shipping them together an imaging things between them. If it had more scenes like kissing or flirting with each other than I would consider it a BL.
Khun was wrong for acting that way to Siwat there at the end. what the father does/did does not go onto the kid…
Sometimes the kids know what their parents did and some even participate in the actions. So Khun wasn’t sure if Sin was apart of anything but since he couldn’t do anything to the father, he shifted his hatred/blame to Sin.