I have lived though the whole is cybersex infidelity relationship problem, and lost my lover and best friend of 13 years in the balance. So, I admit some bias but I have also had 5 years to contemplate what happened and why. Here is my thoughts.

In this day and age, we no longer primarily worry about sexual exclusivity for reproductive purity, which is a large part of what most monogamy and adultery rules were originally set down to enforce.
Today most people choose monogamy because they fear that sexual relationships will lead to emotional relationships, and then the end of their relationship. Unless carefully managed this is often true, and it is as true in cyberspace as it is in meatspace. (At this point someone always brings up the STI issue, and while it has merit, it is for most people an afterthought not a primary concern, which is why STI’s are so common in the first place)
My point is that ANY sexual relationship, be it in a hotel room or a chat room, must follow the general rules for sex of the relationship you are in, be that monogamy or any poly arrangement, because those rules were set down to manage emotional security not sexual exclusivity.

On a side note. Thank you for writing about this, and all the other great sex positive work you do. You are appreciated.