I agree that sex has quite a bit to do with how you perceive the event. That's where I feel quite a few LD's run into the wall...they perceive it much, much differently that their HD partner does. Changing a person's perception of almost anything is a very difficult thing to do.
I know for me when it comes to giving a BJ my desire to do that for my partner has a lot to do with that person in particular. I've known men I wouldn't even go there with...why? Their behavior about it turned me off. I used to gag too because I hadn't learned the best technique for me to use...let me tell you that feeling of not being able to breath when someone else has gotten into the act and holds you there can be a scary feeling, especially when they go too far into your throat. Not to mention that the gag reflex really can and sometimes does kick in...no matter how accomplished you are at giving a BJ.
For some women simply the texture of semen in their mouth makes them gag. It has nothing whatsoever to do with their desire to please their spouse. I used to gag to the point of almost vomiting and I'd have to run for the bathroom to spit it out (I know lovely picture huh?) because I couldn't physically swallow the semen without gagging on it (yet another picture a man would love to see)....it was uncontrollable.
I have since learned the best technique for me to use to avoid gagging...but you know what that took me time to learn. And after having bad experience after bad experience with that I wasn't sure I ever wanted to learn it. I still didn't have a problem giving a BJ, but to the point of completion was a problem for me for a long time. In order for me to learn the best techinque for me to use I had to be in complete control during the BJ...no holding my head down (I still don't like that).
All I'm trying to do here is point out that it's not necessarily a rejection of the man if a woman doesn't finish him off to completion....just giving you another perspective on it since I did used to have a problem with this myself.