I wanted to update to say actually...because I'm proud of this but it's so... crazy.... what I did was make another account that I own that I send emails to that kind of makes it look to me like I'm emailing him (so the pavlovian part works). It's worked really well for the past couple of days. I hope it keeps working. Haven't emailed ex-boss since Tuesday and don't want to nearly as much, or even if I start to, I just change the TO: address to the decoy account.

I especially want to thank everyone for the suggestions that prompted this solution b/c it is something that I struggled with for over two years now. I hope that I'll go back to emailing my boss infrequently eventually and send most of the emails I used to send him to my decoy email address now. No need to reply... but maybe this will come in handy if any of you also have email problems.