Is this behavior cheating?

[H.T-11]

The only girl I've loved, and for eight years became my girlfriend in 2011. She is is 22 and I am 23 and we had all of our future/marriage plans set for 2014. We met in person but she lives in TX and I live in VA. I've just discovered last week that she has been recently messaging another guy on facebook that goes to school with her and that liked her for a while, all behind my back. The messages show that they've exchanged future plans and she gave him her date of birth. When I asked her if they met in person, she said "no".

There was a time when she brought him to her bedroom, she said in the facebook message: "I don't normally do that...It was so embarrassing...I showed you all of my stuff...we went too far". They also went out to eat and met publicly many times. There were also messages where he was trying to push her to accept an engagement proposal from him but she considered the proposal then rejected it. She's the only girl I've loved and I've rejected a lot of nice/beautiful girls just so I can marry her, however, is her behavior unfaithful/cheating?