Makes perfect sense to me, although I think there is more to it. Your feelings of guilt must arise from a breach of the trust your other half places in you, or a breach of the "rules" your relationship is governed by.
Some people don't feel guilt or don't recognise rules of behaviour. They can cheat by cybering too, if they ignore their partner's expectations.
However, I don't think it matters whether you are cybering, using a prostitute, keeping a mistress, or simply thinking about it. You are cheating if your behaviour is unacceptable to your partner.
In the past I have had friendships with girls which my wife did not approve of, fearing my infidelity. Had I even taken those girls out to the pub for a drink without her approval, I would have been cheating.
TYWD