Yes, I have had a similar situation. I worked with a gal for 10 yrs and then the boss decided to retire and we didn't work together anymore. We had become really close, even though she was younger than me, telling each other our problems, etc.
As soon as we didn't work together anymore she just dropped out of sight. I called her a couple of times but she hardly ever called me. It really hurt.
Anyway, believe it or not we are working together again. This time, though, I will not expect anything if we don't continue to work together anymore.
My advice to you is to let those friends go. Concentrate on the ones that respond to you....they are your true friends. I know it hurts cause I've been there but believe me, time will heal and you will put them behind you.