To Befriend or not to..

What is Friendship and how wonderful it is to have people who matter around you all the time is something we all have known since childhood and I don''t see any purpose in trying to repeat it here. But what I really want to know is that, are there some prewritten rules or formula which SHOULD be followed to be someones friend failing which you will be out of their lives, you know the things like:
1.Must call up and talk,share things with them for at the least 'n' times/week.
2.Should go out with them even when you have your own reasons for avoiding that trip.
3.Should meet them every now and then.
4.Should actively "participate" in their discussions.
So on and so forth...someone please correct me if I am wrong...but it seems like IF only these things are followed/done, can we be friends..?!.I have had friends who are wonderfully true to me despite the fact that NONE of the above conditions are met. Cant friendship exist without such stupid rules...I don't see any logic in trying to get judgmental over people who haven't followed those afore mentioned rules. As far as my knowledge goes, friendship should be all about the bonding,trust and understanding not some prewritten rules which can be easily broken when distances matter...
Also, I really don't understand how is that someone who was yours can gradually become alien...how can you hate someone you loved...it feels sick to realize the fact that someone to whom you mattered a lot is actually plotting your course map towards the exit...All this hurts even more when you realize that all along their morphing, you have been the same...I don't really understand why should someone else pay for someone elses attitude change when you have always been the same...
Well...I shall stop this note here before others get an idea of me killing myself..NO..I am fine, just wanted to write this for quite a long time...!!