Leo and Nico are secret besties, it all started on the Argo 2 when Nico saw thought Leo's mask and the two started talking and  they bounded over there similar traumas ( such as lost of mothers,running away from their problems ,and having vary limited friends),and how they both fell for someone who was straight and would never love them. than Nico fell for will and they started bounding over how they are both gay for handsome blue eyed blondes. 

Once they stayed dating those so called handsome blue eyed blondes they told each other first and fangirled about how they were dating Will and Jason. Will and Jason didn't know until one day Will went to go visit Nico,and just to walk in one one of their gossip sections (with mcdonald's ofc), than ran away to tell Jason who didn't believe him, but when he saw it he was happy that they both had another fired that they can talk to.