There are options to remove yourself as a cosigner on your son's student loans. The article linked below contains some good info. It appears, however, that your son may need to instigate the removal of your name as cosigner.
https://pocketsense.com/remove-loan-cosigner-2002636.html
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***