Dear Sushant:
The title of your thread is “Why is it so hard to let go of a friendship?”-
My answer to your question: it is so hard because your craving to feel special, to be attended to in a special way, is a very strong craving. At one time, this craving felt satisfied with this friend, in your interactions with her. The nature of the interaction changed and the satisfaction is no longer there.
But the craving still exists, yearning to be satisfied. Because she is the last person who satisfied it, you keep longing for her and this is why it is hard to let go.
Regardless of the origin of the craving, whether it existed before the death of your parents, or it originated after their individual deaths, made more distressing as you moved to a different country, that craving is strong.
Attend to that craving, examine it, find a way to satisfy it healthily, and you will be okay.
Post again, anytime you’d like.
anita