Can’t get him to finish

The first time me and my bf had sex, I blew him so that he could finish not inside me, and he came. But now whenever we have sex I still don’t let him cum in me, but when I blow him it takes forever and he still doesn’t bust. He randomly told me today that Im good at giving head, so why can’t I get him go cum, and how can I spice it up a bit????

Edit: today i played with his balls and deep throated him, he moans and shows me it feels good but i want him to finish!!!!!!