Farewell , My Good "Friends"

The past 3 Years of my life have gone by very quickly. It seemed like it was yesterday when I first came to the UK and started my University education. In my first year I made many friends and our entire course was so much like a family.It was an excellent atmosphere and I didn't feel miles away from home in a new environment . I could go on about how wonderful the last 3 years have been.. but I shall save it for next year ,when I graduate :-).
We were a group of 4 coursemates, a Sri-Lankan, a Malaysian and a Greek( all guys). For 3 years we used to hang out together, study , exchange ideas and notes, help each other out with coursework, clear doubts ,why we were also lab mates. So naturally there was a level of comfort with each other. We enjoyed every bit of it.
Graduation came calling this year.......................for them. I was the only one among the group to continue on an MEng degree. The truth was that I thought I would be OK with it.......not such a great thing...you make friends and you move on when the time comes.
Two of them left. Sad part was that they left without me knowing about it. Idiotically I visited their flats and found out that they had checked out many days ago. What hurt me more that I was later told of their departure by my 3rd friend.. .
Did the last 3 years mean nothing to them? Not even enough to say bye and exchange future contact detail? Did the fact that I stay on the floor below them not even come to their mind? Not a call .. not even an msn chat blip was sent out to me..
Were they really my friends? Or did I just assume that ! What a fool Ive been ! Words cannot describe how sad I feel....