I am inclined to agree with what many others have already posted here. Each relationship has it's own boundaries which have been established by those individuals.
Whether one is cheating or not, can only be know by that person, however. Even if the spouse/partner does not know about the other's on-line activities. It is entirely possible that they have a "I don't mind, I just don't want to hear about it." guideline that works for them.
In my situation, Sir visits the internet often for his r/p games and has a sub overseas whom he loves dearly. She and I have talked on occasion, and we routinely ask Sir how the other is doing. For myself, I don't care to hear about his r/p adventures much, although he enjoys sharing some of the more "interesting" ones with me.