Is this a trick question? He's frequently a negative pain in the arse who accuses you of cheating if you're not responding to him immediately. You end the relationship of course. And when he asks "why?", tell him that it was because of the negativity, fights and accusations of cheating.
It's important to remember that dating is about finding Mr/Ms Right. It's not about wasting time with someone who far too frequently drives us nuts. And don't EVER continue a relationship with someone who falsely accuses you of cheating.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.