Make cumming more pleasurable for him

Okay me and my SO have a decent sex life. I love our sexy and so doesn’t he. BUT for some reason when he cums he doesn’t feel good for him. Sometimes he doesn’t even know he came. Which I find really odd. Because I lost definitely know when I am because it feels amazing! He seems to like cumming when I’m going down on him. But how do I make it feel better for him while we are actually having sex?