My thoughts are that she was drunk and was justing doing it for the attention, so I wouldn't consider it cheating.
But then again, put me in the situation and I might feel differently.
Don't be a bitch.
@u_i_c: Go to here: http://www.trendsecure.com/portal/en-US/threat_analytics/hijackthis.php
download either one then run the program, click on "do a system scan and save a log file"
After it's done with the scan it will make and open a .txt file with the log, copy and paste...
Obviously because he's got a bunch of insecurities.
The issue has obviously affected this girl, so if the guy cared about it he would understand this and fix his attitude.