1. An intense need for constant companionship or affection.

2. A relationship where one or both people is completely codependent on the other and cannot bear to let them leave their side.
Girl 1: "Aww, that girl from our Spanish class is crying because her boyfriend is out of town..."
Girl 2: "That's total Sad Puppy Syndrome."
by Fireflycities March 31, 2009
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