The feel of this is very relaxed, with the dark, yet not stormy sky; the way Blue is leaned back; and the softness of the general environment.
The transparency of the curtain and the dimness of practically the entire left side mixed with the brightness of Silver's hair attracts all attention to the couple immediately, which is just as well. It allows us to see their passion before seeing the relaxation. This gives off a feeling of intimacy.
One thing I especially like is the railing. Without the railing, this piece would only be half as good, because it provides the necessary depth. I like it because it is subtle. It does its job without calling too much attention to itself.
One thing I don't like that much is the rose on Blue's waist. It looks flat and inorganic and pops out too much, distracting from the more important aspects of the rest of the piece.
It's not especially important that the couples don't have eyes, noses, or any other real features. In fact, I would say it's a good thing they don't. If there was more detail, it would change the mood from intimate to something more... voyeuristic.
I would say that perhaps you should mix up the horizontal and vertical lines a little, give us an angle with a tad more diagonals. That would be slightly more interesting to look at.
Overall, 4/5. A great picture.
For the record, it was Kotone, not Blue...
It looks like it's not exactly a rose, but, say, a flat piece of glass or cardboard painted to look like a rose. And yes, it mostly pops out too much because it clashes with her dress, but also because it contrasts with the drawing like Silver's hair does.
Voyeuristic basically means watching someone have sex. Instead of feeling like they're the only people in the picture (intimate), adding faces would make it so we feel like we're peeking on something we aren't supposed to(voyeuristic).