
Something I noticed is that I'm like 99% sure that the teacher trying to be a homewrecker would hate the mother eventually. She basically creates her own narrative when reality is inconvenient to her, so the teacher saying even one thing wrong and her doing her shit would end the relationship fast. He would probably either hold out until he just explodes on her or would call her a crazy bitch and leave her.
Right now he can only deal with her because he has an image of her as an innocent woman, he doesn't constantly have to live with her, and he has a punching bag (the husband) to deflect onto.

Leon ran away to where he used to live with Cliff. With some of his leftover magic, Leon managed to teleport as far as he could. Here it is revealed that Leon began his bloodshed of monsters when some of them entered the cave, pushing him over the edge. It is also revealed that Leon was never good at magic, but that when he killed monsters he stole their power. This is most likely why Leon had such power before and why he lost it over time. Leon planned to hunt monsters to regain power before he was found.
However, Beryl finds Leon. Obviously it has something to do with Mephisto, as Beryl's chains broke and he can smell Leon's (very specific apparently) scent from very far away. Beryl tries to convince Leon to return, but Leon uses some of his leftover magic to try to stop Beryl. It doesn't work, but Leon's next move is perhaps to teleport into the room where Cliff's dragon body was at.
I do not think the father is some evil guy who straight up abandoned his family. It seems he wasn't ever married to MLs mom, so it's possible he never even knew he had a son. I also think this because he isn't trying to like butter up to ML, and I think someone who wanted to APPEAR like they care would have been trying to win over their kid by now. It's also possible that they were forced apart by circumstances out of their control based on the dream the father had, it doesn't seem like he up and left her, but that she went away. The dream could also be symbolic, but the point is that the father doesn't seem like a bad guy who wants to ruin things or take something valuable, because he would certainly be trying to win over his long-lost son by now instead of wandering around a remote village. Some people here are so quick to be hostile about a new character who hasn't even said or done anything bad. He hasn't even tried to excuse his absence from his son's life like a deadbeat (parents who knowingly neglect their children) or tried to meddle in his son's life, he's just vibing around the village.