The statutes for Criminal Conversation are 3 years from the date of the last sex act. The statutes for Alienation of Affection can be successfully argued to be within 3 years of the time that the alienation is complete, and sex isn’t a required element for prosecution, only that you were the principal factor in the dissolution of the marriage by coaxing her emotionally away from her husband. This means that if you two stay in contact, but she leaves him for you twenty years later, he still techinically could sue for alienation of affection within 3 years of her leaving the marriage.
There have been cases successfully prosecuted where the person returned then left again, but didn’t go back to the person they had committed the affair with. There’s no necessity to prove that the two in the affair are still involved with each other, only that the paramour was the principal cause of the alienation of affection.
If he indeed did hack into her email without legitimate access to her passwords, then that particular evidence is inadmissible. You’d have to be able to prove that he was not given access to passwords or the account in any way, though. Even then, any post-separation contact between you two could be used as evidence of a pre-existing affair.