Know that I will always hold a place in my heart just for you.
I know all too well that guilty feeling of being happy with a new pup after losing one. Duke wouldn't want you to be alone Val. He would want you to have another dog to love and to keep you company. And yes there is a special place in your heart that will always belong to Duke. But our hearts are big enough to love another and give them a place in our hearts without giving up that special place for the other.
I know you must still be hurting so much for Duke. Please know I'm thinking of you. {hugs}