A forgotten birthday

On Saturday when I was travelling in my car I came across a college where my friend had once studied. She was a friend, a roomie and one of the first buddies in an aliented world. I remember her crying when I had to go to my hometown and very excited when I come back. Someone who used to be very much happy with my birthday or any other occasions for that matter.  I used to wish her a day in advance coz I used to forget the date. But this year, I think for the first time she has forgotten my birthday and it hurts.Its as if everyone has moved forward, become busy but I was still in my hostel. I know I shouldn't be sad and just accept the fact that people change but somewhere changes like these hurt