If you're using Mail.app, then it will replace the email addresses of people in your Address Book with their names, but the email address is still accessible. There's no way to send an email without your email address showing up.
I'm not sure that it's anything he's doing. While you have the message open, go to View > Message > Long Headers. This will show the whole traffic of the email including his email address. The Return Path should show the email address.
That looks like a truncation of the address, probably caused by your software. There is a way to hide the addresses of additional recipients, including the sender's address, but that's not what this looks like.