Well....I have 2 yorkies and also like the idea of them having each other for company when we are not home. Even with two, I still feel bad when we are gone for too long, so a buddy for Parker will help ease your anxiety on leaving them home, but not deter it completely. My first yorkie (a male) was almost 2 when we brought our little girl home. At first he wanted nothing to do with her..we even took him with us when we picked her up and amusingly (to us), he would not even look in her direction all the way home. I don't remember exactly, but I'm sure it didn't take too long for them to grow on each other and become best buds!
So I say yes, go for it! 
Do it now so that you have plenty of time before going back to school for them to become accustomed to each other. Then be ready for double the fun and double the yorkie kisses every time you come home!
