I can so relate to this, Tessa our golden cross was destitute when Zack (my atavar) had to be put down. We quite unexpectedly got another Newf rescue, Annabelle, and they are now great mates. Tessa does however still lie on Zack's grave some evenings, quietly by herself. They mourn and she knows we do, because she will sit beside you in a very quiet manner when we are talking or thinking of our dearest Zack. We only had to put him down late may. So it is all still very raw.
They (dogs) also get used to the empty space left behind. Annabelle did not take Zacks place, she just took another space. And she really needed to be loved.
Picture of two new friends