It might not be the sex per se, it might just be that you are past the honeymoon part of your relationship (said to be the first two years, whether a couple is gay or straight doesn't make any difference). I don't think in your shoes I would focus on the level of wetness to determine whether or not it's a happy and fulfilling relationship. Are you two getting closer all the time, and more certain of each other? That is what to be wondering.
This is a hard one. Are you so close that you see her as more than a friend than a lover? Have you been in other long term relationships that remain sexual prior to this one?
I want to offer an alternative perspective here and you can take it or leave it and I might be way wrong. Do you think it could possibly have nothing to Do with her? She’s beautiful and attractive and the other aspects of your relationship are fulfilling, is it possible that it’s you? That maybe you’re feeling down or different? My biggest mistake in my relationship was blaming my unhappiness on my partner because the sex wasn’t passionate enough or he wasn’t sweet enough but the reality was that he put in a lot of effort and I was very very depressed and holding on to childhood agony of being neglected abandoned sexually physically and verbally abused with basic needs withheld at times. I was not passionate because I was not whole and complete on my own. Take that for what it is, I could be way off and if that’s the case I’m so sorry but it seems like you’re looking to your relationship as though that should make you happy but there are so many aspects of your life that just because you’re not happy with your sex life or you’re feeling bored in tour day to day life or not as fulfilled might have nothing to do with tour partner. If they’re putting the effort in and you don’t want anyone else I would think about how you feel about yourself and how the other areas of your life are going :)
am wondering if the long term relationship was with a man, that it might be that in the long run you're more responsive to men than this first experience with a woman?