A very good friend of mine suddenly started avoiding me. Why?

Hi, I am a guy who's working in a software industry. I have recently changed my job for better career opportunity. In my previous organization I had a couple of good friends, both male and female. Even after I left my job we are all still in contact.
I had met this girl at my previous office about some 8 months ago. We both had become very good friends since then. She was a beautiful looking girl. In the beginning I used to like her. But later when I came to know she had a boyfriend I gave up. But we became very good friends. The reason was we always used to leave office together after office hrs. We had some friends accompanying us sometimes but we both used to be there always. Never left without informing each other at least. She is a nice girl and used to be very friendly with all of us, but more with 2 guys of us, and above that with me. I am saying this because she used to share everything about her office problems with a guy from our office none other than me. She had trust in me and I too trusted her always. We had developed a very good emotional bonding between us.
We used to chat after office hours everyday when used to part away after some distance. We both had become addicted to it especially me.
In my last days at office I had become a bit emotional and said her that I will miss her when I will leave the company. She always supported me and used to say we will meet in life later. Now when it was my last day at office, I had bid a farewell to all my friends. I had sensed she had become emotional too when she hugged me before leaving. Later I joined my current organization but we still were in contact and she used to phone me or send me a message sometimes. We were in contact for about 2 months. But suddenly around 15 days back or so, she stopped talking to me. I thought she might be having work stress or something, so I too gave her time and didn't call her or message her. But later on she blocked me from her IM, then she avoided my calls. And later when I had visited my previous office for some official purpose, she even didn't come to meet me. I told her I felt very sad about not meeting her, but she didn't reply. I asked my other friends what happened but they too didn't get a response from her. A friend from our group which used to accompany us told me that she was a little upset since a last few days and used to stay alone. But I didn't get why she stopped talking to me. I tried to find out reasons but got none. I tried to ask her but waste. What left me thinking was that maybe she has got into some trouble in her family or love life because of me. Whatever it is I started feeling guilty for nothing and I doubt she would have shared this with anyone else other than me if I was not the culprit. I don't understand a nature of a girl and maybe a girl will be in a better position to answer this stuff. Please help me.