Sam -
Very beautiful, some masterful melodic writing here. The sense of an unbroken line is wonderful and well crafted. That said, there's three things I want to raise - not necessarily criticisms, just points that you might want to consider.
First, I wonder if it's a bit 'samey' all the way through. As I said, the continued line is beautiful, but I wondered if you might want to shake it up a little bit? To me, the modulation is the perfect point to introduce a different texture. If you would want to keep the melody as it is, which I imagine you do, this change could be something as simple as putting the piano part up like 2 octaves for this section - letting the cello hold the bottom of the music with the piano glittering on top. That leads me onto the second thing: be careful with the registers you're using. Most of the time, the piano is sitting in its middle bottom register, coinciding with the cello and that tends to reduce the clarity of both parts. I think in a live setting (because you really should get someone to play this!) the extra resonance from a real piano would completely overshadow the cello. Just something to watch.
Lastly, a very minor thing, I think the trills/mordents /gracenotes could just be just be written out in full, standard notation. To me, they hold melodic value and aren't just 'throwaway' notes. Of course, you might think differently - and of course, it's your piece! I'd be interested to hear your thoughts on that.
Well done on a beautiful composition!