hello everyone

[loulou49]

I recently took my sons dog in, a cute **** tzu. Very well behaved 41/2 years old. very happy go lucky. i did not think i really wanted another dog after mine died 8 years ago. He is a great companion and we seemed to be great friends. I have had him about 3 months and within the last two to three weeks he seems to have become extremely depressed. listless not eating much laying around alot. not jumping on the couch anymore. the only thing he seems like he halfway enjoys is a walk outside. In my opinion, I think he realized he is not going back to his old home and has just become depressed.
When he is around other animals he becomes more animated. the minute he comes home he reverts to this odd behavior.
I enjoy having him around but I think he is starting to make me depressed because I feel like there is nothing I can do to help him.
does anyone have any suggestions ??