@Kneel_Breen—
Yeah, the proper rule, even when the student is an
adult, is for the teacher not to express even reciprocating interest in a student so long as the student might plausibly think that a grade or the quality of teaching could be affected.
I've no doubt that an adolescent might genuinely love a teacher, and that the teacher might genuinely love that student in return. But genuine love on the part of the teacher would mean not simply choosing to believe what one wanted to believe; genuine love would mean waiting until the student was more surely psychologically mature, and certainly no longer one's student.