It's easy to say that hypothetical questions are harmless and can even be a great way to get to know someone, but there's more to it than that. Hypothetical questions can be approached in a myriad of different ways, and it's up to the asker to decide how they go about asking. That's exactly what Nikhil did in this situation--he recognized that his ex's approach to these hypothetical questions was disruptive and annoying, so he chose to end the relationship to avoid further conflict. It's wrong to think that Nikhil's decision was wrong--in fact, it was likely the best decision he could make in this difficult situation.
There's more to it than simply not wanting to deal with hypothetical questions. Nikhil had a valid reason for not wanting to answer his ex's questions. He felt that she was asking them in a way that was disrespectful and disruptive, which made him uncomfortable. By deciding to end the relationship, he was standing up for himself and for what he believed was right. It's true that hypotheticals can be a fun way to get to know someone, but when they are asked in a way that is disrespectful or annoying, it's important to draw a line and choose not to engage in the conversation any further.
Nikhil should be praised for making an informed, rational decision in an attempt to avoid any further conflict. His breakup may have been seen as drastic, but it was the right move for him. Instead of responding to his ex's disrespectful questions, he chose to take a stand and assert his boundaries. In this way, he showed self-respect and confidence, which is something that should be admired. Sure, hypotheticals can be a fun way to get to know someone better--as long as they're asked respectfully!