By definition adultery is engaging in sexual intercourse with someone other then the spouse. So, technically no but it is dishonest to be doing this behind your spouses back. They should be the one that you are having this "e-fair" with. It shows no respect or compassion for the spouse and it could lead to something else.
Your not actually engaging in sex but it is deceptive to your spouse/partner. Fantasy is a natural think but that happens either alone in your mind or with your significant other. Maybe you can ask your partner to do things that you talk to with the person over the net.
If your lover has no clue you are doing this than it is very dishonest. No, you are not actually having "sex" but you are emotionally connecting to someone, "turning on" another human being. If you think your significant other would disapprove of your behavior than its wrong. If you love that sort of excitement, talk it over with your girlfriend/boyfriend/spouse... maybe you can involve them. You just might have found a way to spark your relationship again. If the tables were turned, would you be jealous? Would it hurt you a little? Would you feel left out?
If my fiance did this sort of thing behind my back I would be hurt... but that's just me.