I'm inclined to agree with Rogoczy here. As I have stated in other threads with similar topics, who in the Hell really cares about the definition of cheating? All it comes down to for me is this: when your partner finds out (note I say "when," not "if"), is the hurt they feel and the consequences of your actions going to be worth the play you engaged in online? Simply, which relationship means more to you?

When your partner finds out, you can give all the explanations you want about how your secret online rendevous are really just legitimate bouts of mental masturbation with another person; but if your vanilla girlfriend is still hurt and opts to walk out the door on you, are you really going to be more satisfied alone with your "definitions" of righteousness?

Up to you to decide that.