Twice. The first time, it was a friend whose live in boyfriend cheated on her and dumped her and we had all been part if the sane friendship group and gone on holiday togetger, stayed in each others' 'houses, etc. . I supported her when she was low and after about a year, during which time I moved to another city, I saw one day that she had blocked me on FB. So i guess she did it because I reminded her of hurtful times, but she hurt me, and I could have really done with her support when I was dumped by my boyfriend from the same friendship group.
The second time was a friend I one through sport. Again, really close friendship, over for dinner, etc. Then they became more successful at the sport (partly because they inherited money to spend on it) and dropped me. They dont bother talking to me at all now. It's actually embarrassing. They've done it to other people too.
Both times, there was definately an element of me being no longer quite cool enough for them and not being exactly the type of person they prefer as friends.
I grew up abroad and I do notice this a lot with British people. I have lots of uncool or, alternatively, very cool friends from my home country that I'm still in touch with, who will always be my friends despite changing lives and being hundreds of miles apart.