SUBREDDIT: r/relationships
TITLE: I'm [25 M] seeing this Girl [24F] for a month, doesn't do oral..
POST: Throwaway for obvious reasons.

Now I've posted here because no, I haven't spoken to her about this and would like some advice.

Been seeing this girl, let's call her Stacey, for about a month or so. She's attractive, great personality, respectful job etc. Things have been good so far, however, we've had sex 10 times so far and every time I've gone down on her for 20 minutes at a time (I have no problem with this as I find it a turn on too) she obviously likes it, but then it just turns into sex. She hasn't gone down on me once yet, which I respect but I'm wondering what's putting her off? I know for some people that's not their thing etc but how should I go about talking to her about it respectfully?
TL;DR: 
Seeing girl for a month, I go down on her every time, having great sex, she still hasn't gone down on me..