Note: This is an extremely long post!
One thing I'd like to stress is the concept of "destiny" and "fate" in this show. It's a major aspect of our lives and it affects our future. I know both of these phrases may be similar but it is only because they are linked. From research, I understand that "destiny" is the destination, what will (or will not) happen. Fate on the other hand, is the path that leads to the destiny. Say for example, we turn left instead of right and meet someone who will change our destiny (yes, I'm using a Doctor Who reference but hush!). Now, our destiny is a predetermined course of events (I believe there are more than one destiny but it depends on our fate). Now if we changed the path of our fate in which in this case is turning right instead of life, we may not meet that person therefore our destiny (and the course of events) is altered.
Anyway, I digress. What I wanted to say is that Asad is Zoya's fate but her destiny is the answers to her unanswered questions. If we think back to the first two episodes, Zoya runs away from her Nikaah to Akram and ends up at the dargah, which is where Asad also ends up. After re-watching it, I noticed how Asad is directly in front of Zoya but yet does not notice her until she is in tears. Now, people often go to a dargah to pray and although we don't know what Zoya is praying for, I assume its about finding help in either getting away from Akram or finding her Abbu. Many people I know have said that if you pray with a pure heart and with emotions, your wishes are often fulfilled. This links back to Zoya's tears, her helplessness and how in that moment, Asad sees her (I know Ayaan also notices her but I'm going to ignore that for now atleast), a symbolic link that Asad is the one who will help her. But yet fate does not stop right there: Zoya and Asad meet each other a few times until she arrives at his house to stay. It is fate that led her there, as its a coincidence that Anwar knew Dilshad.
I think that although Asad was the one that pushed Zoya to meet Akram, if Asad was not in the picture, Akram would still have done the same thing: only difference is that Zoya would be stuck in a terrible situation and no Asad to help her. But yet that goes for the mangalpur fiasco as well. One of the things I believe in is that we, the people, are sent to Earth to accomplish something. If we think about it, we are born at a certain time/year and to certain parents. Although we might not do something extravagant that will change the future like inventing something (okay we might do) but it could be the little events that we do, that changes someone else's fate and ultimately their destiny. In link to Qubool Hai, if Zoya never came back to Bhopal, never met Asad, never coincidently went to Mangalpur, she would never had met Mariam and helped her. For all we know, Mariam could have actually burnt herself or murdered by her family. I guess on a greater scale, we could say that if Zoya never had the questions in her mind (who was her father? what happened to him? or in reality, her mother?) then all these things would never had come into play. And I guess (whilst I'm digressing) if these things never happened then Asad and Ayaan, the only link (so far) between the Ahmed Khan/Siddiqi households, would have yet till this day become separated (I'm assuming). And who knows, without fate being fixed, what if their destinies were altered?
Now coming onto the present events, Asad once again implied that he IS Zoya's fate through the coin tossing scene. Asad is not the person who would lie as it'll go against his principles but yet he lies that it was head instead of tails. I don't think it's love for Zoya (at least not yet, and even if it is, he himself doesn't know it) but it's his genuine feeling and emotion that he doesn't want her to leave. And though Zoya believes her Abbu is "dead", fate - as in Asad - plays against her. Zoya's Abbu chapter has been closed from her point of view and the door to New York, to her other life, is open. But yet, she asks Asad whether he wants her to leave or not, making him her fate once more. And of course, Asad says "head" meaning he has changed her fate and therefore her destiny. If we think about it, if Asad told the truth that it was "tails" then Zoya would have left and never looked back about her father or Asad in that case. But he didn't. Meaning her unanswered questions WILL be answered because of Asad being the catalyst.
Finally, I'm not exactly sure about the current track with Asad-Zoya's fake engagement as it's just started, I would assume that Zoya's fate has again come into play (provided they actually do get engaged) changing her destiny. This could go in any direction, if Asad-Zoya get engaged then it becomes a fixed part of their life as I don't see them getting engaged for fun and if they have to get engaged/married under the pretence of her visa, then it will end up serious. That's just one theory but it may be that their "engagement" leads to Zoya having a lead onto Ghafoor (perhaps unknowingly), again symbolising the fact that without Asad, this would not have happened.
There are many scenes and events that suggests how Asad is Zoya's fate and how he is the catalyst in her finding out about her Abbu and what happened to her mother. Even if Asad and Zoya do not get together in the near future (if, according to the Zee synopsis that she marries Ayaan), we shouldn't forget that Asad will always be in Zoya's path regardless of her destiny. One more thing I would like to add is that destiny may be altered depending on what we take, if she marries Ayaan, therefore fulfilling part of her destiny, if the marriage is dissolved, her destiny is instantly altered (unless the same paths are walked across again). Ultimately, Zoya will never be "apart" from Asad even if both of them are not together or are with other people, because as from what I've seen, Asad and Zoya's paths always meet.
I guess this somehow highlights the meaning behind Shakespeare's quote "a pair of star-cross'd lovers".