Guitar Practice - 12/17

I had slightly changed my goals this week because instead of going over music theory, I wanted to get some tips for playing by ear. My goal was to play with Alexander in a few weeks time, but because Alexander is quite the accomplished musician, I'd have to find out what I'm supposed to do. I soon discovered that I have no business holding a musical instrument. I can not tell the difference between two notes, almost entirely. I thought maybe I could work on this by either practicing or maybe there were some exercises I could do to train my ear. So far, it doesn't seem to be working.