I haven't had birthday greetings in a long while, but I already got used to not being greeted on my birthday. Even if FB has a reminder, it's not as if my "friends" care. After all, these people have other priorities in life than learning about my birthday. In short, just don't expect anything in return. If you beat yourself up over it, you will only make things worse for yourself. I once tried to be an attention-seeking person, but now I consider myself a loner, and it's not so bad actually once you start getting used to it.