I can definitely see that unnamed guy taking advantage of the daughter, getting her pregnant, and abandoning her, making her into a psycho mom and repeating the process over again.
Also, I think the manga is trying to show that everyone is at fault here. The teachers for pressuring the father without giving him any guidance or support. The company which expects him to keep working like normal after the fathers tragedy. The father for letting himself get involved with a minor, he should’ve just cut it off at the beginning. The daughter for always running away and, opposite to what she said, never trying to understand or be there for her father (just because she is a kid doesn’t mean that her actions or lack of actions don’t have consequences. Also, give 16 year olds more credit, they’re selfish but they’re not that stupid that they aren’t responsible for their choices. Most places will try you as an adult in court at 17.)