It's immoral to abandon unwanted pets.
Carrie adopts a cat and then realizes her boyfriend is allergic.
Carrie wants to make her boyfriend comfortable in her home.
Carrie calls the facility she adopted the cat from, expressing her problem to them.
Carrie drives the cat to a wooded area and leaves it behind.
The facility offers to take the cat back to give it to another interested family.
Carrie feels terrible guilt at abandoning the cat she just adopted.