Well, to begin, although this is only a sketch I do feel this has a great impact potential. What I do like is the textures and the grey, cloudy sort of atmosphere brought on by the shading and tones, as well as the raggedness of the clothing. I also /adore/ your ladies face, complacent and almost seductive.

Most of what I feel needs the most work is anatomy, in general. Your males anatomy is pretty spot on for the most part in the torso length and muscle placement. In his left arms position, though, I thing his pectoral would not be overlapping his shoulder muscles. Also, hands being as long as the face would be a good rule of thumb to remember-- though his hands are curved and such, they do come off a bit small. Your ladies proportions are a bit on the long side as well, since women generally have shorter torsos, longer legs in comparison to the male form. Since she seems to be a tall girl, bringing up her hips would do wonders, and centralizing the bellybutton would help her look much more sleek, since its falling a bit low here, though its only a minor detail and all.

The bigger issue, I feel, is his face and head structure. Contrary to how lovely you did the ladies, his is a bit lacking. The back of his skull is placed quite high, and with the addition of his short whispy hair, makes it seem much longer. The connection of his neck to his head is a bit thick, and bottlenecks near the center, where it should thin upward gradually toward the head. His face placement is somewhat low, giving him little room to have a chin or a jaw, and I was slightly confused by the expression made by his lips. (Unsure of if his mouth is open, or his upper lip is there, or?) If you managed the back of the head and brought the face up a tinch, I think it'd be much easier for you to map out his expression from there.

All in all, I do feel the emotion you were striving for was there, and I think if you keep at it, and grab up some references or do figure drawings prior to your next endeavor, all of these crits could definitely be remedied. You are lovely with technicalities and your shading is top notch. Hopefully this is a style you develop gradually and continue to evolve with over time! Good luck!