From the settings application you can go into the Privacy option and turn off location services. You can also go to the "share my location" page from that "location services" page and disable the option to share your location.
Though if he has access to your Apple ID he can use the Find My IPhone website or application to track your phone. To disable that you'd go into your iCloud settings from the settings application and scroll to the bottom and disable Find My IPhone. Remember this also prevents you from locating your iPhone if it's lost or stolen though.