In psychological concepts like "Lust" the correct meaning is in the context it is written. I clarified mine in my first post, now if you think lust is only about sex in a relationship then I don't think I wanna change your belief or opinion.Lust can have different meanings for different things like lust for money etc. But my dear lust in a romantic relationship has only one meaning and that's strong sexual desire for someone. And nowhere in this show Mishaan have been shown having lust for one another.
Lust means strong desire for something, Ruhaan has that desire to have mishti, if this was normal couple, with this desire, he would want to sleep with her, sex is a part of relationship, he doesn't get to do because mishti is engaged
Mishaan do have sexual desire for one another, their all scenes are about physical proximity, scratching ruhaan's chest, "don't look at me like that", caressing his shirt, I am yet to see ANY sort of emotional bond