Basically she is a teacher with " passion" for teaching. At the age of "15" she shd have guided her student to complete his education at any cost first and then think about other things. When she realizes infatuation of one of her students aged 15, she was ,"25" quite old enough to understand the implications. In due course too she just gives her love as "excuse" as her co worker rightly points out. Age gap might not be deterrent but in that case both shd be ADULTS with their heads firmly on their shoulders. Here the boy is still high schooler? Fanning his feelings is CRIMINAL. She shd have refrained and guided him properly as TEACHER. Rather than doing the correct thing she keeps on justifying her misendevour. Plus she had her ex by her side who has been shown to be a dependable rational person. Rather than going with him this selfish in late 20s teacher keeps on seducing her student!
Irrational and criminal!
It seems that rather director WANTS it this way just for (?) cheap sensationalism.