Frankly the best part about this drawing is the shading since it was executed next to perfectly as it's really given a great sense of depth and form to both figures. What really bothers me, though, are the hands, especially the blonde's hand that's grabbing the boy's elbow. That added to the blonde's arm that seems off propotions. You were probably going for foreshortening but you've executed it incorrectly. Don't take my word heavily, but if I were you, I'd try to add some drop shadows behind the arm to show that it's away from his side, and edit the contour so it'd look like something like this
Maybe the hand could be even bigger considering the head's size(hand should be as big as the head). But that might be just me being nitpicky.
The
[insert impossible-to-pronounce name] in the blonde one wasn't drawn right as it goes from the very bottom of the ear to the very top of the sternum which isn't what was done in the blonde one's neck. And for the ear itself, well, you could just refer yourself to your own ear or real life pictures.
The rest is all good. I really like the picture as it has got some warm and fuzzy intimacy feeling to it. I get that from the brown haired one in especial. Really, good job for what you've done.