I have been there and it is hurtful. I just left Spain after 11 years and only one person writes me. I was so suprised and hurt because I thought I had some good friends.
The best thing for you is to focus on the friends that do stay in contact with you. The others, it is their loss. You are a special person and they are missing out by not staying friends with you.
It is dissappointing to think that people are friends only to find out that they really aren't. I think most people only have a few really close friends and the rest are just aquaintances. It is good that you discovered this now before you put any more of yourself into the relationships.