I also agree with her about the tagline "Mohabbat ke jahaan". It means this past is not gonna come to change their love, but their situation and circumstance under which they are in love. The atmosphere, their surroundings, people around them, everything will start becoming different. Right now they are showing how their closeness is being developed by being alone together, being cute with each other, etc. But I guess Love has to come from deep within. It has to be fully passionate and intense. And this past will make the surroundings such a way that their falling in love will be much more intense and meaningful.
I dont think this track will bring in more problems for Zain and Aliya. Otherwise, they wouldnt be together in this.