Um, well, I've actually been in a situation where my cat was the love of my life, instead of the person I was in a relationship with, so I can relate to Ethan.
My favorite part of the story is the suspense you build while we wonder if Christine actually killed or deliberately lost Butcher. I also like the play on words when she says "I lost it". Does she mean she lost the cat, or that she lost 'it', her temper or her sanity?
One possible change that would make her character stronger, perhaps, is the simple deletion of the word 'accidentally' in "What if I told you I accidentally killed your cat?" If she just says "What if I told you I killed your cat" then she is really mad (or really crazy). In my experience, a mad girlfriend wouldn't hedge.
Thanks for your reading, @cliffagreen :)
I like what you suggest, remove that "accidentally." It would definitely make her seem more evil, at least while we suspect she may have actually killed Butcher.
Sure she was mad, and I think Christine really lost her temper, too, even if she didn't kill the cat.