slwatson LGer
When I had 5 adult society finches, they had all sat in the petshop for a long time and bonded. When I added a 6th from a private owner)to even it out they treated excluded him from everything but nightime in the nest.
They are very into their "own group", like cliches, and I noticed my CackleJax getting more and more sad and depressed.......although he did EVERYTHING to be a part of the group.
I lost 4 of those 5 finches almost overnight and good ole CackleJax stepped up and raised 7 of their kids, with the help of a strange finch who he has since pair-bonded with
I would get a smaller cage (and another society finch male or female depending on your breeding status) and let the "outcast" form a new relationship with a new finch in another cage.
OMG that finch will be reborn! Good luck to you!!