Can I use an extra bluetooth with macbook pro retina? I'm using a bluetooth earphone very often. It works really well with iphone and ipad, but it just doesn't work well with macbook pro retina 15". The range and connectivity are pretty bad. 

I'm thinking about buying an external bleutooth adapter. Can I use it?
Yes, as @Buscar웃SD said, you can use an external Bluetooth adapter. On my Macbook Pro 13" I had to use Apple's Bluetooth Explorer to set my USB adapter as the active controller. This page describes how to download and use Bluetooth Explorer.