Damn this is good. A deeply emotional piece that had me enthralled from beginning to end. I loved every minute of this, and I'm not even a fan of chamber music. Nice work!
You truly have a mastery of the harmonic language of the late romantic era, would you mind breaking down some of the techniques you used? For example, during the first minute or so you clearly establish F minor as the home key, then venture off to many foreign harmonies before returning to F minor right before the cello enters. Would you mind breaking down what chords you used and how you came up with them?
As far as constructive feedback I don't know that I have much to offer. The piece is great as it is and I don't see any real weak spots. The only thing I'll point out is it seems like the first theme is given alot more emphasis than the second theme. Specifically, the first theme takes up the entire first six minutes of the piece, with the second theme first appearing around the 5:55 mark and lasting until about 8:30, when the first theme returns. After this, the second theme doesn't return until 11:33, lasting only until 11:50, and it appears once more from 12:38-13:33. So the second theme only gets 4 minutes out of a 14.5 minute piece, while the first theme gets more time than that it it's first statement. Maybe this is your intention, and if so that's fine, just my thought from a few listen-throughs.
I also had a few questions about how you made the audio. Did you record yourself playing a live piano, or did you use a vst? Also, did the cellist record himself in a hall, or did he record dry and add an artificial reverb? From a mix standpoint, it definitely sounds like the two of you are in different rooms. You can tell at the beginning that is sounds like you are playing in a small intimate space, then when the cellist comes in it sounds like he is in a much larger space. As a result it sounds like the piano is right in front while the cello is farther away. If it were me, I might try to mix it so it sounds like the cello is close to the front (since he is the soloist) and the piano is a little farther back. This is purely my subjective thoughts, it sounds wonderful as it is.
One more thing I might add is the pizzicato in the cello near the end was a little "boomy", and the last note was not quite together. Other than that, a spectacular performance from both of you.
Thanks for sharing!