In my opinion, its not about either Mahaan or Stupid, Harish is just sparing her for being hurt in the long run, it is not as if he is suffering from a minor disease, having brain tumor can be fatal, so if he hides the fact from Avantika and tells her he has moved on, she is going to be hurt, but since she has been living without him for 20 years now, she will be upset for a while but then she will also try and move on, but if he tells her the truth about his illness and gets back together with her and later on something happens to him, she will loose him all over again, so which pain would he rather give her ? ? Sometimes its not about the wrong and right decision, its about taking a decision which will be less painful for your loved one.
I knw a person n real like dis...He hided his illness(cancer) from his wife and son 4 not bothering dem and 2 avoid 'expenditure" ...becoz it was sure dat he will die..he was not from a financialy well family...so if his family came 2 knw dey will sell their home 4 finding money ...moreover his son was n 10th or 12th..so he didnt want 2 bother him..Only n his last days his family came 2 knw all dese...
Though he needed 2 tell his family n long run it helped his family alot I thnk..