I think it is important, and I think you should not be grossed out.
If you are happy with him going down on you, and taking in your fluids, then you should not insult him. You should do the same. Your hang-up is actually saying you find a part of him gross and disgusting. Can you imagine if he said you taste and smell funny down there, and he does not want to give you oral ever again. He did it one time, but he was so shocked by it, he can never do it again. You would just laugh at him, and maybe you would not have kept seeing him. Why should you be any different?
Pardon the pun, but suck it up babe. Bite the bullet. Take it with a chaser. You get my point??
Yes, it might taste gross at first. So does cough syrup, but after a few days, you can stand the taste of cough syrup. I suggest you do the same here.
Be fair, if you dont go down(and all the way) then do not expect him to do it as well.
(of course, I do not mean this should be done every time and all the time. He does not have to cum in your mouth every time, that would take the fun out of things. Sometimes get him off, and let the spunk go else where. That is of course you are looking to get him off by oral sex alone, and you do not plan to have intercourse.)