I definitely have a close relationship with my instructor too Stormy Blues, but the important thing is that she was my instructor before she was ever my friend. I know that she knows worlds more than I do when it comes to horses, and that when she says I'm not ready for something, I'm really not. But taking the same advice from someone who was your friend first and instructor last means that they were your equal before they suddenly became your superior... and that can sometimes get annoying for riders.
For example, I often try to give my sister pointers on how to correct a little something here or there in the way that she rides... and try as I might to say some of these things in the nicest possible way, she still usually gets quite pissed at me. The same goes for my mom, and even I'm not very good at taking lessons from my mom.