Sorry to read about Ping.
Siamese do pine more than other cats, and I know its a bit soon, but have you thought of adopting?
It might help you both, I know it helped me and my cat (now RIP) when it happened to us some years ago.
Tigger walked around the house for weeks calling for Sooty, and a new younger cat helped take her mind off it.
I felt guilty at the time, but I couldn't stand to see Tigger so upset.
Look at it like this - you are not being disloyal to Ping, you are helping another cat, which in turn will help you and CoCo