The Strong, Silent Type - S4-E10
Revealing mistake: Christopher is high from shooting heroin and sits on Adriana's dog and kills it. She comes home and calls for the dog and sees her under Christopher. He picks her up and you can plainly tell its a stuffed dog.
Answer: That's not Jimmy, just a look-a-like. Jimmy's short and stout, the guy in "Christopher" episode is tall and medium built. The hair is also different.