Ow Man that's hard but things in life are not permanent, the only constant in life is change.
there are times when you're happy and there are times that you need to say Goodbye.
Learn to Move On.

You could try to save the friendship but if that doesn't work you need to widen your circle of friends so that you won't feel so bad after you fall out with one of them.

It is really very painfull , but we must trat with our reality...u must do the best to keep this friendship but if there is neccesity to separate from your best friend you must do or you you will lose him/her by time.so it is better to separate with respect way.

If it is a good friend to good tolerance and does not leave go

Yea, am experiencing this feeling right now, the person who used to be my best friend is going away gradually..our friendship lasted more than 13 years, we promised to be friends till the end of our lives..
But... the spiritual distance began to grow when she left school then when she got engaged, she no longer has time for me, I understood that it's a bit normal to change then, but not that way. It's really hard to say good bye, I couldn't and I still have hope that she will come back...though she's going to marry this summer and I am not acknowledged of the date yet, and she will live in another city..
Anyway I am obliged to admit and accept this, it would be very difficult...

u'll believe me If I told u that I separeted alot and in another way I leaved my city and came to another city(Its the capital) and another school so I saw diffrent people and diffrent students with another thoughts and I was more than shocked cause not only leave my friends no and see also diffrent (may be i can say)culture.really it was so hard to accept this,and everyday I was back from school It was just like that finally I backed to somewhere I know.and even I always can make alot of friends,I just couldn't,they weren't like me.and the people who were like me and grew up with them in amoment they aren't here.but u know I just found the way that I can accept that and have alot friends without changing myself for them.and may be It was my turning point cause now I know how I can be a friend to everybody .but I wanna tell u something,even if u'll be so lovely,there would be some people just see that u r selfish and don't care about anybody and u can separate them easily.
then I believe that u don't want to separate u can save it,but that If the (another person (the other side)) also don't want to separate