I had one dog for 3 years. When my boyfriend moved in, he brought his dog with him, and we panicked and schemed about how to introduce them in the park, and not bring one into the other's territory etc. (mine being a protective German Shepherd). Anyway, turns out, they get on like a house on fire - such different personalities, but best of friends. And I feel much happier going to work knowing that they both have company - leaving one dog on their own all day is horrible, I used to feel so guilty if I got stuck in traffic or something on the way home. I'd say - Get another one! (and wait until after Christmas and go to the local pound to get an abandoned one to a good home).
Best of luck