Couples Disease 

When 2 people (both in seperate relationships) are so used to being in a couple that they are adapted to being in a pair. If the other half of the relationship is not around, then the person will try to form a pairing with another person (preferably someone who is also in a relationship). This pairing usually contains no sexual activity, but will usually contain some "snuggling" if it is an other night situation.

These people (ever since being in a relationship) crave being in a pair. This will mean that in groups of 3, if there are 2 people in a relationship and one person who is single, the two people currently in a relationship will attach to each other due to the fact that they have something in common (the fact that they are both in a relationship). This will leave the person who is not in a relationship left out of conversation (see "Third Wheel).
This leaves the single person to realize this, and will give him the urge to write this on urban dictionary (because he has nothing better to do and is single...)

You cannot contract the disease without being in a relationship, as you don't feel the NEED to bond (that doesn't mean they don't WANT to form a bond though...)

Mac is going out with *insert girl A's name here
Mia is going out with *insert boy A's name here

Mac and Mia decide to snuggle up together for the night leaving *insert lonely person's name here* on his own for the night. Lonely person realizes that Mac and Mia have Couples Disease

Couples Disease by DMAN03 July 13, 2012