The first question needs to go to you:
What did you intend when you "reconnected with an old friend?" Did you want to be friends? to be lovers? to break up his marriage? What were your expectations? Do not feign innocence here. You did not want to be just friends. If your intentions were "honorable," you would have emailed to his home. You expected or at least hoped for an "inappropriate" relationship.
Next you need to answer your desire for the next step:
Do you want to be "his lover" or to "break up his marriage?"
This is not about him. It is about you.
YOU initiated contact.
YOU maintained communication secret from his wife.
YOU avoided conversations about his wife.
YOU intended/hoped to get here. Why are you rationalizing now? If the benefit to you exceeds the pain to him and his wife, you should go forward. If not, run away.
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The real best answer to this is for you to GO OUT AND GET A DATE WITH A SINGLE MAN!
If 2 years after your divorce, playing "you've got mail" with a married man is the best you have done, you are not trying for a satisfying, fulfilling, life-long relationship. Examine yourself and your motives.