OK let’s take the equation of “I” out of this discussion, since we are discussing the “cheating” aspect we will assume the question is “am I cheating when I have an on-line relationship?” This is going depend on how your partner feels about it. A person will be threatened by different things and at different times depending on circumstances in the relationship. I have seen heavy flirting by one partner be a real violation of trust to another. This is what it really comes down to, is there a violation of trust? And come on this should be no surprise to anyone who has conscience, if you are hiding any type of relationship from your partner then odds are good it’s a violation at some level.
So to the question is it cheating? I would say if your partner knows and is OK with it then no. If you are secretive about the activity or your partner knows and is bothered by it then it’s a dishonest situation that will only lead to a relationship breakdown.