Yeah, it is cheating, however... all drinking, just a kiss... meh, give her a bit of hell, if she sticks around maybe she learned the lesson.
Although if she is proclaimed pansexual (what happened with bisexual?) it does make her a huge hypocrite when she gave you shit for your question :P
Now what you might want to consider is that, how serious are you about it?
If you are serious and she is "lustdriven" you will might a bad time.