Well, the answer is as simple as it is complicated.  It totally depends on the nature of the relationship you are currently involved in.  If the current boundaries of your relationship do not exclude such behavior, then you are not cheating.  If your significant other (SO) would be upset to find out that you have been carrying on such a relationship online, then by definition, you are.  If you don’t know what the boundaries of your relationship are, then perhaps a little more communication is needed between you and your SO. 

One thing to always remember is that relationships online are no different than relationships in person.  Think also about the same behaviors you are engaging in online and imagine that you were behaving the same way toward someone you knew in person.  If this would be viewed as cheating, then the same behavior conducted online would also be considered cheating. 

It basically comes down to the One Question Rule of Relationships, which is really simple.  Ask yourself one question, “How would I feel if my SO was engaging in the same type of behavior?”  Odds are, if you would not be happy about it, they probably wouldn’t be either.  If it wouldn’t bother you, then you need to communicate with your SO and make sure the two of you are on the same page. 

So, just remember, it all comes down to the boundaries that have been set in the relationship.