Ofc he would reject her. From adult pov, they are student-teacher, ethically and morally speaking it should never go beyond that. But he really didnt have to lie, just keep it at 'friend' instead of fake girlfriend. Also I do have issue her coming over to meet the teacher during an off day, if she's mature enough she should know it could be a troublesome thing. But then again, she's still a teen and he's her first love so its understable the emotional turbulence she's experiencing.