How do I make my boyfriend want to go down on me?

My boyfriend and I Have been Dating for 6 years and he has gone down on me only like 5 times since we been together. Idk what's the issue because the times he has have been great and he looks like he enjoyed it. I go down on him every time we have sex and when I don't he asks me why I didn't like if am wrong for not doing it. What should I do?