Will I lose my best friend?

We always need friend in life, and then we finally found our best friend, when we met someone who care, understand and accept us with sincere feeling, no matter with many of our weakness.
That's happen on me, I found 2 best friend in life, I share manything wit them laugh together, support each other ang give care to them. But today... I just feel I finally will lose one of them, honestly feeling break up inside.

A friend that I met here, when we are come to this country as foreigner, not much friend we have. Even we seldom meet physically but we talked a lot through net. Twice a day we said hi, talked about manything, shared joked, and when one of us got in to problem, we supported each other. But there is time to meet, there is time to say good bye. Finally my friend complete study and go back to the country origin. My Friend promise me nothing will change, will always contact me everday even a few minutes.

That time i believe, after went back for a month I still receive mail or chat at least once a day, even only 15-20 minutes. Then the following month it reduces once on 2-3 days. I tried to sent short message by mail, but sometimes i got no reply. And lately not on 2-3 days but 4 days with only words "hi, how r u, hope everything ok with u", no personal and freindly message anymore.
Become worst the last month that contact me only twice, no mail reply.

Could someone change easily? Many memories gone, and pretend nothing happen. I feel it will be hard to have a best friend again, if then will end up just like that. I thought I never change still the same, never judge my friend, even when I sent mail without reply, i try to use cherish words. I pretend nothing happen between us, but this I got. Will I lose my best friend?