We just belonged to the same school and organization so it's his loss not mine anyway... This is the second time I've dealt with being unfriended on Facebook, but then I'll get over it and I'll ignore him as if we don't know each other.
It's only FB but I know the feeling. Perhaps, they get too busy to pay attention to anything. Someone unfriend me but still stay in contact via other form of technology. I give him the benefits of the doubt all the time though lol