I am really sorry for your loss. My cat, Nyska, went through the same thing when we lost our St. Bernard, Lilly. They loved being together and nap together. After Lilly died Nyska was inconsolable, meowing and going all over the house looking for her friend. Try giving your Jaden lots of attention and time. It will get better for him in time. He is mourning for his sister. Maybe in time, if you think it is right, you could adopt another kitty. It will never replace your Jaela, but it it might help you heal. Again, sorry for your loss.