My baby uses my nipple as a pacifier....

My baby is 3 months old and uses my nipple as a pacifier when he is done eating. He can be on one side for almost 45 minutes, but only really eating for 10-15. How do I change this? I’m worried when I go back to work that he won’t sleep during the day because he doesn’t have that. He also won’t take a real pacifier 😕 Any advise?