I basically agree, in a weird way, that the deception necessary for betrayal puts it into a different category than openly pursuing other people.
There is something to the claim "I didn't mean to hurt you", pretzel logic it though it may be, that differentiates cheating from unilaterally, and openly, declaring the relationship open.
And the sort of person that would make such a crazy unilateral decision openly is someone who is not a hypocrite (which is something we all are to some degree) but both declares and acts in a manner contrary to our values. There is nothing to resolve because it's a fundamental misalignment in values.
A cheater at least declares adherence to shared values but acts in a manner contrary to them. Here there is something to resolve. If we choose to believe a hypocrite is willing or trying to reform, then we can become aligned in behavior. We can seek out the patterns of thought and behaviors that the hypocrite has used to justify their actions. To identify them. To reform. To do their best to live up to their purported values.
I think if the switch to deception never occurs, most cheaters wouldn't cheat. They would openly share their feelings, identify they are not appropriate, and avoid the slippery slope.