I really don't understand him very much because I like giving orals way more than receiving them. But I can give you my perspective. It isn't the flavor of the fluids what I love (it's more like an acquired taste really). It's the intimacy, the empowerment of making your partner climax in pleasure, the worship of her body as is, and her juices as the most pleasant substance. That and other psychologic causes make it great to me.

So, first of all the physical part. Did you taste yourself? What color and aspect does your fluids have? It's sticky? Maybe there is really a problem and your boyfriend has no way to know.

Second the psychological aspect. You can tell him something in the lines of "show me the way you like/love me" while you show yourself your genitals. Do it sometime he is not expecting sex, like in the kitchen or something. Refusing in this context is almost impossible, because it's like a challenge and he will accept.

Then, don't verbally teach him, physically move you or his head. Enjoy and make sure you have an orgasm, doesn't matter if it takes time, don't worry about him. Meanwhile, show how much pleasure you feel. You will boost his ego.

After this, compliment him about how much pleasure you had but mainly how happy he makes you feel when he only focuses in you. But don't have sex, nor reciprocate in any way.

Still, don't ask for oral sex during sex. He has to learn that it's a token of his appreciation to you, not just something to do before penetration.

Do that when you see fit and the guy will feel super powerful for making you happy and probably turned on for the way you casually demand it. After some time, that will enjoy eating you more than he likes a BJ.

Good luck!