OTP

The concept of OTP (One True Pair) was not created by any member of the Squad, simply originating on the Internet (most likely Tumblr). However, it has been applied, most commonly to Nathan and Brandon and occasionally other pairings. It is used to signify when others wish to see two people be together as more than friends.

Nathan and Nick
The story of Nathan and Nick as "OTP" is a fairly short and one-sided story. It is mainly due to Nick being accused of practicing Nathanism.