My problem with the concept of cyber being cheating is it implies neither partner can have separate friends of their own... and certainly not friends of the opposite gender. Because 'thinking" and "flirting" about someone else in real life is no less a fantasy than doing so online. More in fact...

And if it is cheating, then the old argument that reading men's magazine is also cheating. Looking at another woman in sexy clothing on the street is cheating.

I know a lot of people will say it's not the same... but I suggest it's just a matter of degree.