I agree with May, IGNORE THIS EMAIL. Pretend that he didn't even write it. And even more importantly, pretend that you never read it (ie, don't change your behavior based upon this email).
He is acknowledging in writing that you are plan B and you have already decided that you do not want to be plan B.
Can you get out of the house and GAL today? Can you go NC as much as possible over the next few days? He is likely going to ask if you got his email. What is your response going to be?
