[spica308]

Tharun asked one final question. 

This is just a What if question. Think and answer: Okay, we started our life now, you are forcing yourself out of Jay circle. What if Mithra comes tomorrow and wants me back? And I have to leave you? Will you be able to convince Jay to take you back? Do you think he will accept you?”
Nikitha looked at him for a long moment, then stood up and started walking back toward the villa without answering.
Tharun rushed after her, gently stopping her. He told, its just a What if!!
Nikitha replied calmly, “Before taking the flight, I already moved out of Jay’s house. I’m staying temporarily at a women’s hostel. Maybe I’ll make it permanent instead of shifting between you two.
And for the record, I guarantee you — I won’t stand in the way of Mithra.”

And Nikita never misses her word, her promise.....She doesn't have strength now to take more guilt for break other girls heart by stealing his man.....she blindly believed all this time that Tharun will take care of everything....She believed Tharun's word that Mithra never responded his love, she believed Tharun when he said Mithra is Jay in his relationship....

Of course this is my guess and what I understood from the plot....whether she will breakup with Tharun seeing how messy he handled Mithra or not, whether she will reconcile with Jay or not, whether she will live alone as she said without both men or not, or whether US/UK trip will be the plot to make Jay and Nikita bond again or not....we have to wait and see....

~RCF

Heygi has alluded that he is not thinking where Nikita will end, only she will be happy and will keep people around her happy. She has not been very rational in her choices, but has kept her commitment to Tharun.
Tharun is not comfortable with the depth of her relationship with Jay, that is probably the reason for writers stress on "transparency". This transparency bit is unantural or may show the control Tharun has over her. May be she is worried about being misunderstood. 
The leeway she has given Tharun was never given to Jay.
Change should be for better, not for sake of change.