You might activate Chaperone on his cell phone without his knowledge. Then you may track him from any Internet computer.

Or just follow him in a friend's car that he wouldn't recognize. The key to this is maintaining a good distance. Only close enough to track where he goes, but not so close that you get spotted. This is called Private Investigating.

Do so cautiously, there may be strict privacy laws where you live. The law is sticky when both parties are adults.