I think this is the story of The Worst Girlfriend Ever. A woman sold her boyfriend's dog while he was deployed. 

Robert Gabbert is a soldier in the U. S. Army who is currently serving overseas in Afghanistan. When he left, he asked his girlfriend if she could please take care of his dog, an adorable Shiba Inu named Baxter. She agreed, he left and then she promptly sold the dog on Craig's List to a family in Colorado, claiming that the dog was too hard for her to take care of.

Robert placed his own Craig's List ad (that has since been deleted):

I am currently deployed and my ex sold my dog. I just found out and I am trying to find the people (person) who bought him. I will pay anything to get him back. His name is Baxster and he is an Shiba Inu. I do not have my phone with me. You can email me. The phone number is my mom’s she is helping me locate him. If you have any information PLEASE give us a call or an email.

When the family who bought the dog was approached to give him back, they said no because their children had "grown too attached" to the dog in the month that they had had him.

His plight was picked up on the local news as well as social media, and a "shaming campaign" went into full effect and the family has now agreed to give the dog back and Robert's father is going to take care of the dog until Robert comes home.

Robert's father has also agreed to purchase a new dog for the family that bought Baxter because he says he "feels bad" and that the kids "should get to have a dog".

It's good to see this story have a happy ending!

Has a significant other ever sold something of yours when you weren't around?