I agree that this story already burned its suspension of disbelief rather early on, but I feel that if you don't take it to seriously it has its charm.
I wonder if page 18 was a jab at studen/teacher stories or more of bit of a reallity check to the audience for them to not mix fiction with reallity, and that that kind of relationship aren't at all like a manga or something.
Anyway I think probably next chapter won't introduced a new girl and will rather re-affirm the first girl feelings, BUT if new girls get introduced I would also like a delinquent and/or gyaru like a couple of comments mentioned before