I did the same thing. We have the sweetest most docile 4 year old yorkie, and I often worried that he was depressed by being a lone dog. So we got him a little brother!
Cooper wasn't ecstatic about being a big brother, the new baby "Baron" has a LOT more energy and jumps all over Cooper while he's trying to nap. BUT when we took Baron in to get his neuter and puppy teeth removed, he had to spend the night at the doggie hospital and was gone a day and a half. COOPER was depressed and kept looking for him in his crate!! Here we thought he HATED his little brother but it turns out when we brought Baron home from the Vet, HE COULDN'T HAVE BEEN MORE EXCITED!
Point of my LONG story is: I had the same fear. But dogs
are pack animals, and if you give them both attention (remember it's like bringing a new baby home, with a toddler already!) Your current dog will love having a companion
