Interesting question...
Well, I would say it´s cultivation. Example of all: Pay attention to flowers, plants, garden, family etc to keep them grow healthy. It´s same example with our friendship.
You don´t have to write everything into long pages when you have hardly time. It would make you tooo tired to write everything like this to keep the friendship often. That´s why we didn´t do it.
(I am lazy writer lol but she knows I didn´t forget her since I was pretty busy with my life as same as she do with her life, too). It´s important to know that we didn´t forget each other.
Well, what we did to keep our friendship long is kept in touch each other by send short messages. I´m happy & satasify with those short messages because it shows that she didn´t forget me until we have time then write everything with the news until we bought fax machines...
We contact each other quite often through fax. I can fax her anything what I like during good or bad day until we bought computers.....
We emailed each other almost everyday with short messages through computers. I would say that I prefer computer because I feel she´s here with me when we are on line to chat.
That´s what I mean about "cultivation" is take care of our healthy friendship. :P