Why you don't use people
In the movie Harinder deliberately used Lajjo, to get free food, for himself and his friends, since he knows the girl likes him and will do favors for him.
He does this even though people keep telling him the girl likes him. And he replies that he doen't like her. She even stops by hie house one evening with sweets for him. He getts his sister to retrieve the sweets and lie saying he is not home. But he grabs the sweets and eats them anyway.
Now later on in the story Lajjo has a chance to help Harinder reunite with Aayat, and instead she burns the letter that would have reunited them.
Now I would have resented Lajjo, if she hadn't been used by Harry. She always thought he had liked her first and them Aayat got in the way. That is why she reacted the way she did.
Which is why you don't deliberately use someone who cares for you. Be Honest with them. You never know you may need their help one day.