Dog likes to go off by themselves

I have a four-year-old male Shih Tzu who just started (1-2 months ago) going back into my wife’s office when we are out in the living room. We are just sitting on the couch reading and such. My dog goes to the back of our house and either lies on the floor or on the futon in my wife’s office. If we get up to do something, he is right out front immediately. A lot of the time, except in the evenings, he will be out with us, laying next to us or on the couch near us.

Another weird thing, our former dog (he passed about six years ago) would do the same thing. My wife and I are the only common denominators, but we cannot figure out what we are doing to induce this behavior.