I read everything you posted and I think I can shed some light on the situation. Now i'm no expert in Astrology but I know a bit, so I'm going to try and help you here.
Being an Aquarius female myself, I instantly recognize some classic " Aquarian " ways with your gal. We Aquarians are in the category of Air signs. Air signs are known to be somewhat "Flighty and with our heads in the clouds" at times. All the flip flopping back in forth that she is doing is something that as an Aquarians tend to do. Granted, that is a stereotype but it seems to be consistent with the sign. Now when you say she seems at times "disinterested" That is another Aquarian trait. We really are not the most emotional people, we tend to come off cold and are not exactly the easiest to have relationships with because of that. You then say she will be completely into you at points and once again that is the flighty nature of air signs.
You being a fire sign makes you extremely passionate and you delve into love and sex with everything you got. From what I can see that is why this is making you so crazy. Her naturally Aquarian ways tend to often confuse you because of your straight forward style.
Now because of the situation that you are both in, that is also making it awfully hard on her obviously. There is a marriage involved and she feels guilty. Completely understandable and normal. That is definitely one of the main reasons for her actions. However, I probably know better than anybody that you cannot help who you fall in love with and have feelings for and that is what makes this such a touchy and emotionally charged situation for the both of you. I can somewhat understanding where you are coming from on this. This is a sensitive situation and therefore that can make people do crazy things and often lead to confusion.