@dreamfall,
Unprotected oral sex is a pretty common activity. I don't remember ever being in a sexual relationship in which I haven't both given and received oral sex. I have never used protection for oral sex... I know the term "dental dam" but I have never seen one.
This isn't very risky behavior, and I can't speak for everyone... but I think unprotected oral sex is a part of most modern sexual relationships.
Of course, if you regret it, then don't do it. But, I wouldn't worry about it.