The other issue with intellectualising infidelity in a relationship (as opposed to listening to your emotions) is that it’s underpinned by a belief that you’re rising above these socially constructed emotions - you sound like you believe you are more “awakened / woke” than someone who reacts emotionally to a situation.
However your core feelings seem to more aligned towards wanting monogamy. Otherwise why rationalise this as an addiction to treat ?
Sounds like ideally you would like to work through this issue with a view to returning to monogamy. You don’t actually seem to really want an open relationship. Either he is dishonest or has a disorder & you alternate between the both.
It’s like you’re ashamed to admit that you prefer old fashioned daggy monogamy. That being too emotional is a negative female trait & you want to rise above your socially constructed emotions to a higher ground.
It is totally possible to believe in open relationships without wanting that for yourself. It’s like supporting LGBTQs but not actually identifying with it for yourself.
You still have not answered whether your partner would tolerate this behaviour in you (sorry if you have & I missed it)
As Oprah would say, what is your authentic self ? Your emotional construct of a “perfect fairytale” relationship does not really sound like it includes visions of opening up your relationship. While I think the fairytale is naive, the reality of your relationship is at the opposite end of the spectrum.
Assuming he works outside the home he could easily take a day off, or go meet up with someone else on his lunch break. Cheaters will find a way, they always do. Incredibly naive to assume he has no time to cheat & that you have an overview of his personal finances down to the dollar. You seem pretty clear you would not snoop his messages or invade his privacy, so how would you begin to find out where his money is going ?
He will carve out some personal time & then lie saying he went to work that day...He is a proven liar & you don’t want to check up on him.
I predict by the end of this relationship you will feel worthless & your self esteem will be shattered. This is how nervous breakdowns happen - one day your intellectual & emotional struggle will cause you to implode. Like your brain will short circuit because you blew the engine overthinking all this & ignoring your authentic self.
I think realistically you need to adopt a ‘Don’t ask don’t tell policy. Turn a blind eye & be happy with your lot. Don’t waste time with couple’s counselling. Just stop thinking about this & get over it basically.
Many people would not stand for this, but many also enjoy their lifestyle & are willing to turn a blind eye. I would say that is arguably more old fashioned approach, due to divorce being viewed negatively in society.