Actually, I don't think this was a judgmental article, it was just factual. The author is specifically talking about cheating, not open relationships. Cheating involves lying. Once you are lying to a partner - and breaking the agreements of the container - then it is very different from ethical non monogamy (where people are in agreement).

This actually isn't complex, and the author is correct that it prohibits full intimacy. In your situation, you may be fully justified in having relationships - intimate and sexual with other people. You and your partner could discuss this and agree, as well as agreeing on the parameters, type of non monogamy, etc. This is very different from "cheating," which involves lying to the person.

If the partner is unable to consent because they are mentally incapacitated, then it is up to you alone to define the parameters of the relationship. Again, not cheating.