In their character profiles you can find their ages, the teacher is 36 and the student 18 (so there's an age gap of 18 years, but he isn't a minor anymore soo it's not illegal.... Well if they weren't teacher and student at least 😅)
(I'm confused about the sleeping together part as well, but I think the translation is a bit wrong or sth bcz I don't think that happened since the dad is straight)
I need more cute bl to read >.<