Jayson Williams was a rich, famous NBA star ... but he tells TMZ Sports, his job running an addiction treatment center is the most fulfilling thing he's ever done.
"This is the best job I ever had."
It's no secret that Jayson -- an All-Star who played 9 years in the league for the 76ers and Nets -- struggled with alcohol abuse for years, leading to tragedy off the court ... before buddies, Curtis Martin, Charles Oakley and Chris Mullin convinced him to enter rehab back in 2016.