@gruffalo5, please believe us when we say that he gets it. He is playing you.
This is absolutely an emotional affair. The hallmarks are there: dishonesty, secrecy, frisson, emotional intimacy/reliance, over-frequent contact, and the trampling of your feelings and boundaries. It is your H who is trashing your marriage and family.
He is clearly obsessed with OW, and they can’t get enough of their mutual validation. Just as he is invested in channeling his emotional resources and spending as much time with her as possible, he is equally invested in gaslighting you to protect their illicit relationship and keep you in your lane. He knows very well that he is transgressing, but will never acknowledge that. His agenda is to lie, downplay and manipulate.
I echo @FairyMaclary‘s suggestion that you read Not Just Friends by Dr. Shirley Glass. She explains the damage done to a primary relationship when a partner opens a window to a third party that results in confiding, blurred boundaries, and a transfer of focus and energy to the new person.
After 2 years, H and OW are way down that slippery slope and have built an intense connection that is not platonic. Their dynamic is ‘coupley,’ and even though you’ve not yet seen a blatantly flirtatious or sexual element, they are enjoying a buzzy frisson, playfulness, and deep closeness. Besides all the day/night messaging and their interacting at work, I would assume they’re having 1:1 lunches and other meet-ups, and pair up during group outings. Their colleagues will be well aware of what’s happening between them.
@gruffalo5, H has unilaterally changed the marital parameters, and you are not irrational or controlling by expressing your feelings and asserting the boundaries you signed up for. It is disturbing that you are taking ADs to cope with the trauma he is causing, and that he suggested it. Stop listening to his lies and abusive, gaslighting tactics. He is determined to keep OW, but you don’t have to stay with him under such destructive and corrosive circumstances. I wouldn’t. I would drop the rope, gray rock him, and consult with a solicitor to investigate my options.