Most people go through what you described, but you should not let it put you off meeting new friends. Personally, as I got older, I learned to handle such situations by treating each day as it comes, and appreciating each day those good things that I have. I no longer take for granted anything I have, nor expect it to last forever (in fact I expect them all to come to an end at some time or another).
It's hard to take this kind of attitude, particularly when you are younger, and more vulnerable to loss, but by treating good things on a day to day basis certainly lessens pain when it does occur.
Write to your friend, and remember she is doing what is best for her. Try to be happy for her.
And don't forget you have many friends here too, for when you are feeling down.
