A very beautiful pice!
Some critiques: the biggest one would be, give the girl whites in her eyes, especially because the dude has them. It just looks odd...
Two, do more smooth shading in the hair, (the skin is all smooth shading, and Most of the hair has no shading) don't be afraid to use rather dark shadows.
One last thing I caught, look at the girls head where her hair curls in, then look at the pocket of skin caught in between, I'm pretty sure thats your skin base. It just looks odd.
I'm trying to be helpful, it is a very good drawing!