Why do two persons come so dangerously close ...
only to shockingly diverge?
The divergence, more so, not because of physical separation;
But due to the loss of respect, liking, face, whatever.
Not necessarily relationships of a romantic nature.
Even the best of friends fall prey to this universal phenomenon.
People change, and we change too.
Guru Dutt to Waheeda Rahman (from Kaaghaz Ke Phool):
Do log ek doosre ko itna accha kyun jaante hain?
(Why do two persons know each other very well?)