Technically, there are a few things I'd like you to consider. The first is that realistically, this is a piece that however simple in appearance is only fully playable by the small population of pianists that have both enough finger independence to do triplets against straight eighths in a single hand (particularly with the reach required in m45) and at the same time have the width of hand to reach middle C and the Eb an octave and a third above it with the thumb and 4th finger (or even more impossible, the third beat of m23). It's a good effort, and a good thought, that you're trying out counter-melodies but it'd be valuable to study the keyword work of Bach and especially Chopin in this case to try and figure out the cleverest and most effective ways of introducing counterpoint.
Other things to experiment with might be approaching the waltz rhythm and feel in a different way (Chopin's waltz in A minor op. 34 no. 2 is a perfect example; all of these pieces can be found at
the Sheet Music Archive), or maybe even having fun with the waltz beat (hemiolas are fun;
Brahms Waltz in B major). One shouldn't feel so constrained to such a typical formula of a single line in the right hand whilst the left hand holds the oom-pa-pa, which is not to say
avoid it, but especially when aiming for a "valse triste" such a formula often ends up making the desirable result more difficult as it can begin to sound so much like your average parlor waltz without particular flair (a more unique sound, and once again I cite Chopin's op. 34 no. 2, can make such a profound effect while retaining the waltz feel).
I don't have very much specific critique for this piece but I thought I'd mention the above in case it'd help.