Sameer and Anand - 2 men, whom Naina loved and trusts most, She loved them equally ( this it true), but when the time comes to choose, she chooses Chachaji over Sameer. Why? She knows that like chachaji, Sameer will do everything for her. Like chachaji, Sameer will protect her, like chachaji Sameer will love her. Then, where is the difference ? Difference is in her life when her father has almost disowned her, Anand took her reponsibility. It is parents' duty to do everything for their child and it is the child's Haq to get that but if someone else does that for him/her it becomes favour not haq. So, for Pooja and Preeti which is haq, for Naina that is ehsaan. That is why she worship Chachaji as if he was not there at the first place, she will have nothing in life. To be very honest, she knows it deep down in her heart, that if Anand did not give love and shelter, then topper Naina would never be there. Sameer is her love, life, reason to be happy everything but Chachaji is her messiah, who protected the unwanted child Naina, like his own princess. How can she choose Sameer over Anand. She walked in the relationship with lots of baggage and burden but Sameer walked in the relationship free of any tie rather with blessing of his messiah, Nanaji and Naina's Chachaji is against it.
The moment Sameer will realize this truth, he will understand Naina's point which triggered her to choose Anand over Sameer, there will be no MU left in Sameer's mind. They both love each other very deeply. They knew it. That's enough. Their understanding will be strongest.