cat's-paw
A person who is used by another to achieve some end, especially in a duplicitous or cynical manner. Taken from a fable about a monkey who uses a cat's paw to retrieve chestnuts from a fire. I thought that Jake really loved me, but in the end, I was just a cat's-paw so he could stir up jealousy in his ex-boyfriend.
cat's paw
A dupe or tool for another, a sucker, as in You always try to make a cat's paw of me, but I refuse to do any more of your work. This term alludes to a very old tale about a monkey that persuades a cat to pull chestnuts out of the fire so as to avoid burning its own paws. The story dates from the 16th century and versions of it (some with a dog) exist in many languages.