Dear Vishal:
You wrote: “(I) loath myself for not being able to be a friend who stood by her unconditionally expecting nothing”- it is not in our nature as humans to expect nothing from a friend. It is in our nature to expect something in return, to give and receive. It was a reasonable expectation on your part, that she inquires how you felt when you were sick, for example.
“how can I be a better person if such situation repeats itself. How one can care about other person unconditionally without being demanding and bitter?”- by giving and receiving as is reasonable. We become “demanding and bitter” when we give without receiving adequately. See to it that there is reciprocity in a future friendship, or any relationship, and you are way less likely to be demanding and bitter.
“to what degree I was at fault”?- I would say it was both of your faults to have stayed in this friendship this long. Both should have ended it early on. Instead she disregarded your feelings as she, for one, went on and on about her crush and you continued the communication with her even though it was hurting you.
Friendships and relationships otherwise need to be Win-Win prospects, giving and receiving within reason. That friendship was not a Win-Win. Eventually it became a Lose-Lose.
I hope you feel better and please do not hope to suffer (“I hope I suffer enough for hurting her”). Suffering will not do you or anyone any good.
anita