I’m so very sorry that you have been confronted with this op. It’s such a hurtful betrayal. And particularly shitty of a bloke during those very hard early child-rearing years when he should be invested in his family first and foremost, and acting as a solid back-up to you. He should be ashamed of himself.
It’s very callous behaviour on his part to have taken something precious between you and sullied it.
The issue now is one of trust. And how do you want to proceed?
I am afraid that I would now be asking very direct questions about those “occasional runs” they go on together. ( I’m sorry but you need to know if they have betrayed you physically too. ). What did they do on those runs? Swap haikus?
I think I would present this to him as his one and ONLY opportunity to restore some integrity to your relationship, by telling you the full truth now, and nothing but the truth, as he must know how painful it was to have been gaslit for all of this time?
(Obviously you are just saying that to get him to confess fully and you can decide independently what to do once you have the full picture.)
I’m not sure that I would whether I would want to stay with a man who behaved with so little inner moral strength though. He’s a weak toad. He’s kept this secret for a long time so you need to decide whether you can trust him again. Especially when you confronted him with it previously and he still chose to carry on.
Also, it’s a lot easier to confess and live with oneself if he can frame it as “only” an emotional affair in his own mind. I have my doubts I’m sorry to say.
Above all op, proceed with huge caution. Look after yourself. Gather support around you, Try to eat and drink properly. Keep strong in front of him. Get your ducks in a row in terms of bank accounts and financial papers. Be prepared for the worst. And be distant and cold with him. If he can move out for a while that would be good. Put a solid barrier there until you know what’s what and protect yourself because he is not who you thought he was. 💐