I know how that feels...
Just try and remember all the good times you shared, the presents of Mice & and Birds dropped lovingly at your feet, the scratched wallpaper, the shed hair all over the carpet.
And as far as Sam is concerned, he'll be with your Dad now, probably looking down on you and wondering what all the fuss is about.
They've only moved on, and I bet they haven't gone anywhere bad.
Regarding what you're feeling at the present, I promise you things will get easier with the passage of time.
What you must do when you're ready is find another Pusscat that needs looking after.
Actually, forget the above. The right Cat will find you, and when it does don't think for a minute that you are replacing your last bestest friend in any way.
I know it hurts when you lose a pet/boss/employer/master/ tyrant, but there are hundreds of unwanted Cats that need homes and I think we should do everything we can to make the ungrateful sods welcome.
Best wishes from...
Ian, Marlene, and Annie the 15 pound Gin Queen Tabby.
(We're convinced she's a reincarnation of Bessie Smith.) P.S. Capri Uni got it right.