If you hacked into his computer that is a crime. If he foolishly let you have accesss, it is not.
I imagine the police may conclude this is a private, not public, matter. But.....if you are asked to come in for questioning, hire a lawyer to accompany you there.
Reading his email is not illegal if the acces was permitted on your computer without hacking into his account. Recording conversations without the consent of all parties to the conversation, however, is a violation of the Illinois eavesdropping statute and constitues a criminal offense. Your boyfriend would be well-advised to stay away from the police with that tape...and you would be well-advised to stay away from him.