Zubair entered the show out of the blue and tried very hard to get close to the Abdullah's. He used everyway possible to get closer and he was willing to do anything. While some would say that he was just trying to be nice, I don't think so. Why would he come and stay at their house, just like that? Why didn't he leave after a few days? After he had been kicked out of Barkat Villa he still helped Aliya design Zain's cabin. He knew that Surraiya doesn't like him and Aliya together, but he still kept it all a secret.
Even after he was released from jail he went back to Barkat villa and helped Surraiya ruin Aliya and Zain's life. That Aliya and Zain who were with him when no one else was, who helped him when no one else did and why, because of a visa? I can't believe that. So here's a theory I've come up with.
Zubair entered the house with the motive of coming very close to the Abdullah's and probably staying in their house with them but when he didn't see that happening and when Surraiya kicked him out in Osman's presence he thought of taking revenge from the family. He couldn't harm Surraiya directly, so he caused Osman's accident but he dropped his watch there. Poor Zubair was caught and arrested. But Aliya believed in him. She helped him and he once again saw a chance to mess with the family.
He is helping Surraiya so that he can go as far away as possible and maybe even blackmail Surraiya after this. He can get his visa, a lot of money and not even blamed for a crime that he did. What else would he want?
So my question to you is, do you think Zubair actually tried to harm Osman? After the sudden change in his character, don't you think he was evil from before only? Maybe that was the reason they got Zubair into the story. He wanted to separate Zain and Aliya and Rehaan is actually in to play the hero?