Past is passed...You can't change it...It can't come now...so there is no threat whatsoever of "it" coming in the way of your "present state of being!" - Unless you allow it to - by thinking about it!
Envy over another's past is actually of no use...
In the context of the story, Aarti knew very well about Yash and his love for Arpita. She also knew he would never be able to forget her. She accepted him only after being aware of this. So where is the question of envy.
Prashant might have said what he did...but I think it is not difficult to move on with the present as that is the truth of the moment. Dwelling in the past is only going to kill the joys of the present.
If at all - one has to see what Yash will do when he gets to know of Aarti's past as it had truth that was hidden!