Since I have watched the movie for multiple times, I can say that Kundan did not cause Jasjeet's death, he just spilled the truth about Jasjeet's religion in front of zoya's family, it is zoya who is responsible for the death, she planned to cheat her family, convinced Jasjeet to lie, manipulated kundan in convincing her own father for the marriage, heck her father wouldn't even agree if not Kundan would have listened to her plea. Kundan fixed her marriage, decorated everything by his own hands, only because she had asked him, he was in peace that he will not get her, but she betrayed kundan by lying, she betrayed her father, she created the whole mess, jasjeet died and because Kundan was the better human being amongst them, he lived every moment with guilt and despair.
Kundan was murdered by zoya too, this woman killed both the men, just the difference is one of them was literate and still fell into her trap and the other one knew that she was planning his murder and still went to get killed just for her sake. Blaming a teenage kundan for stalking is fine, but saying that an adult and educated Zoya was better than him is unfair, she was the villain of Kundan and Jasjeet's life.