When there is true love and sincere affection present during a hug, one head will touch the head of the other. This is even true across species. When the love-affection being expressed is towards a non-living thing - such as a trophy, there is often an emotional nonverbal display with a "head-surrogate". LeBron James (above), Chis Bosh and Dwayne Wade (both below) are exemplifying this body language behavior with the NBA's "Larry O'Brien Championship Trophy". It's as if they are hugging their wives/girlfriends.
In addition, note that the first two images were snapped with James' and Bosh's eyelids being closed. Ninety percent of our sensory input is visual. Forty-percent of the mass of the human brain is dedicated to the vision. Thus when we close our eyes, a bit more blood supply and oxygen get directed to the other four (non-visual) senses as well as the cognitive and emotional centers of our brains. During a sincere hug, we want to drink in the full emotion of the moment - to feel it at its maximum, so we close our eyes. If eyelid closure during hugs begins to wane or is lacking - it is a strongly negative signal of impending relationship failure.
Analysis # 1423: Head First Affection & Head Surrogate Hugs
Analysis # 771: Ann's & Mitt's Affectionate Hug
Analysis # 2: Body Language of Blake Lively & Penn Badgley Strongly Suggests an Impending Break-up in Near Future