Abena888
Hi Abena and welcome to the Forum from Canada.
Regarding George...
Would you happen to know how old your two boys were when you first got them?
I am wondering, if we might not be dealing with old age (?)
Now a lonely finch, is an unhappy finch... and an only finch, is a lonely finch.
Finches, and in particularly Zebra and Society finches, are extremely social creatures, and don't do well on their own.
That said, what then is going on with George?
Is he missing Fred? I would say yes, without a doubt. He is probably even grieving his friend's loss in his own way.
Is he sick? Now that I honestly can't say.
For the time being, I would offer him a warm lamp (40w bulb regular desk top or goose neck lamp is fine) beside one corner of his cage, with shade on the other side.
When birds are a bit under the weather, they find the warmth and light very comforting, but we also want to offer them an area to get away from the heat source if they get too warm.
I would also offer him his favorite foods, spray millet, egg, greens, etc. along with a swing if he doesn't already have one, and a mirror for company.
If all is going well, in another month or so, I would suggest getting him a friend.
If and when you decide to get a companion for George, we can discuss the best ways to introduce them.
Until then, keep a close eye on your little boy, and let us know how he's doing.
Best wishes, and good luck.