Dogs can very easily get jealous if you give them a reason to. After all, they are highly affectionate and loving animals but they need to feel loved too. For better or for worse, dogs need frequent shows of affection to feel loved – if you just ignore your dog and assume that he will automatically know that you love him, keep in mind that’s not necessarily the case.
So, a major part of getting your old dog get along with a new puppy is ensuring that your first dog never feels a lack or even just a decrease of love, appreciation, and security. This means several things:
Make sure your older dog’s territory isn’t too infringed upon
Keep your old dog’s favorite toys away from your new dog’s reach
Give your old dog lots of company, pets, treats, and attention – more so than before if possible
Make sure at least one family member sleeps with/next to your old dog at night
Do these basic steps and you should be able to minimize your dog’s jealousy. Then, just help your two dogs to enjoy each other’s company.