You did a good job of finding the best composition. A square works well for this. Notice how dog and child form two shapes that swirl around and into each other, reminiscent of a yin-yang symbol. Note also how both of their faces actually distort as they press into each other. All these things suggest a merging of sorts, and that promotes the theme of love.
You got a complaint about the child's eye, but to me it represents an altered state, a meditative state, as does the closed eye of the dog. It is almost as if they form a new creature, with one eye from each of them. The boy's other eye seems to be looking not at us, but at (or into?) the dog. Of course, none of this esoteric hogwash was actually occurring, but it is implied via the illusion that is photography. Your other shots, taken of the same event, probably have completely different feelings to them. I think you made a good choice.
Now, about your DPC score. First of all, 5.5 is a great score for your first submission. Since the score runs from 1 to 10, 5.5 is the exact middle, but keep in mind that ribbon winners are generally in the low 7 range, so you only have two points to go! :)
So, how do you get those 2 points? One thing is lighting. This looks like it could be camera flash. That almost never works for DPC, unless it's "fill flash" used in conjunction with other lights or natural light. In general, you want to see your subject well-lit before you press the shutter. Another possibility is to put the camera on a tripod and use a long exposure. This will create interesting effects with both lighting and motion blur (hint: the DPC voter hates interesting). In both cases, make sure the white balance seems right. (This picture used a flash so the white balance is perfect.) You can correct white balance a number of ways in post-processing.
The other issue is composition, but I'm not going to tell you how to ruin your great sense of composition just to get a high score in some silly on-line challenge.
The expression on the pooch is just adorable, but it looks like you caught the boy at an awkward moment. Great close up shot of the two... you can definately feel the love :)
There is something funky about the boy's eyes that really throws off the mood of the picture. He almost looks demented. haha but I really love that the puppy is closing his eyes its very cute.