Firstly I don't support Karan and there have been times, wen even I have got irritated with his foolishness but blaming him for everything wat happened between him and Teja is wrong.
Teja is no mahaan and she has repeatedly said crap about Shamita and have tried to associate both Karan and Shamita together, she is the reason Karan and Shamita couldn't be friends.
Karan has many times told her sorry and she has behaved like 'I don't give a damn' to you or your sorry's. Karan has lot of times tried to make things fine between Teja and others saying Teja is young don't take her things to heart or forgive her.
They both r same in the relationship and if it's toxic than both are to be blamed.Teja is not dumb though behaves like one whereas Karan doesn't behave like dumb so he gets stuck.