Ramping down? or not?

I have been finding myself more and more confused lately about my romance with D. Sometimes I really feel like winding down the whole affair; other times, not at all. The thing is, I have no idea why.

In favor of winding down: I'm still troubled by my brother's tepid (and almost disapproving) reaction when I told him about D, though to be fair I have not asked him since then if I read him right; I found myself worrying (when she bought Christmas presents for the lot of us) that she was trying to insinuate herself farther into my life than I was comfortable with (though it turns out I was wrong about that); I find her high energy levels exhausting, and I can feel as if I have to keep insisting on limits to preserve a little space of quiet that is my own..

Against winding down: the sex is always fantastic; my reasons for breaking it off are often weak (as I've noted even in the above paragraph); and D can still pull me out of myself and away from my preconceptions ... even (or especially) when the "certainties" that she is overturning are things I tell myself to make me doubt the relationship. (See here and here, just for example.) So maybe it's just my depression talking, and I don't really want to wind it down after all.

I wish the hell I knew what I want.