Lost Friends

I feel weird. Do close friendships last? They do supposedly. Why are they not close now, perhaps life has drifted them away far away from me? Or since i am a student i got more time to spare to keep in touch compared to them? I hope that last question is true.
I have many friends, many of them actually come and go, few only have stood beside ever since i was in my younger days till now that oso not all.
When i was in CSS active and all, i got many friends some were happy to have a fren like me so much so they have expressed it through their mails thanking me many times and also over msn and stuff. (not bragging n nothing about gf bf issues here) They became close and we did work closely together. We enjoyed it. I was glad i had been a good fren to others and also glad to have them as fren for they too have tought me alot. So i also tot that our friendship would last but it did not happen.
On the contrary they have now drifted away from keeping in touch. No more replies to mails, no more hi over msn or sms. What happen uh? Did i do something wrong or have I become of no use to them or were they faking it and do not know how to cherish those gud times? Or perhaps they wud say their life moved on? Even if it moves on i dont c anything wrong in catching up right?? Once in awhile keeping in touch or so.
I am also surprised that those who were not so close as compared to the others instead keep in touch with me although we have not met for a loooong time face to face. To my surprise there are those who seeked me to be fren keeps in touch with me more often, and i have met that person only once! that oso i still cant remember!
What is going on? Is there something wrong or is this just natural??
I think its due to work - TIME the usual devil. Cos those people i mentioned are already working and perhaps they feel i m just a student so a gap has been created. Hahah work oso i am still elder then some of them. Some are working and still keeping in touch!
Sometimes i also wonder - some of these guys who are keeping in touch with me - how long more will they do so??? How much should i keep them in heart so that later i wont get hurt or disappointed.
Should i treat them as case to case basis, when they smile i smile when they dont i dont?
Keeping in touch are at least a couple of months once would give each other positive energy and encouragement whereby you will know you were not forgotten and the sense of appreciation of past close friendships are still remembered. So i feel keeping in touch is important.
haha some people suddenly become close then suddenly dissapear. sigh ....
How am i to reciprocrate. Guess i should go with the flowlah.
It was written somewhere that i would have only few stedfast friends and i guess that would be good enough for me.
hahha sometimes i want to talk crap with them oso cannot end up talking serious stuff pulak ... dahlah org panggil aku uncle huhuh hehe
Is it difficult to hold on onto relationships till at times u get tired ... and want to drift away ...? Or does people think staying in a relationship (not gf bf) is like holding back oneself or getting oneself tied up to the other?
Well all i am asking is to keep in touchlah and dont get the feeling of being forgotten despite all the apraisals given when we were together. Makes them fake pulak d.
But i softlah - wont go hard on them perhaps they just busy.