it's hard to say goodbye, not only because you'll miss your Shih Tzu, but also because you may be exceedingly worried about your dog becoming so stressed out that he does damage to your home, eliminate inside the home and/or bark incessantly.
And when you come home, there may be out of control excitement. Some dogs that suffer anxiety when owners are away simply can't handle the overwhelming emotions of when they finally return. The dog may have excitement urination and/or have a hard time working himself out of a state of excited frenzy.
You can help your Shih Tzu handle your departure and arrival with grace. The key to this is to never allow your dog to think that your presence or lack of presence is a huge event.
Hugs, kisses and play time should be done well before it is time to leave. After your dog is tired from the brisk walk that you give to him and he has had plenty of your attention, you should leave your Tzu to occupy himself in his designated area while you prepare to leave. Act casually around your dog as you get dressed, have breakfast and go about your daily activities.
When it is time to leave, do not say the word "Goodbye" , "Bye" or any word that implies something sad is about to happen. When you depart, distract him with a fun toy and leave while the pup is paying attention to it. Some owners struggle with this.... feeling that perhaps it is 'wrong' to not say goodbye. However, if a dog can be desensitized to when an owner leaves and when she returns, this can help stop the buildup of stress.
Do not worry that your dog will spend the day wondering where in the world you disappeared to; he will simply not go into a state of anxiety based on the fact that you slipped away. If you make your dog aware of the moment that you are leaving, this can trigger a response that can put the dog into immediate panic mode.
Arriving back needs to be handled without fanfare as well. Against all human instinct to run over to your dog, enter the house, take about 5 minutes to read your mail, have a drink, straighten up and then greet him. Your arrival back should be a peaceful and calm event. After this 5 minute slow introduction back home, you may go for a walk, play games and give your dog as much attention as you wish. Your Shih Tzu will then not connect your arrival back with attention and helps a dog control his emotions.