Many women search for proof of infedelity when an affair is suspected.
In reality they are searching for proof of fedelity, you already know he has been unfaithful emotionally, he is capable of lying every single day for years, why would you believe his claims of not being physically unfaithful.
I know it's unbelievably painful and your mind is adjusting to this shock, but do not let him lie anymore, that's enough now, he has decieved you and your children for long enough.
Please believe in yourself and do not allow him to gaslight you, as this is abuse.
In time you will see you are trying to gaslight yourself to help you cope, please be kind to yourself, you did nothing wrong except marry a weak man who has no morals or integrity.
You are worth so much more, and in time I believe he will regret this, but this is his mistake and soon enough will feel the pain of his actions.
Here come the consequenses, he's just trying to prevent them.