Reading some of the stuff about sex can gross you out!
First, you don't have to do anything you don't want to do.
Not everyone (goes down on, has oral sex with, however you want to say it) their partner.
Normal is different for everybody. What seems normal for you might be freaky to somebody else. And believe me, there's A LOT of sexual activities that are WAY more gross than that!
How far normal people go....well that depends. It should be comfortable for both of you. If you don't want to do something, don't do it! Everybody's different.