Partial answer (working backwards):

They took from me something near to my heart. I crossed the Atlantic, my short became long, but I was still essentially myself.    
>! Not sure.  
  
I gave up heroin. I introduced my companions to my friend Syrah.  
>! Syrah = wine (thanks Stackreader!), so latter clue should point to "wined". Heroin could be 'H' (thanks Deusovi!), making beginning of clue "whined?"
  
Once accustomed to a life of comfort, I left all ease behind. I had no place to rest, but I was always of two minds—to meander in and around the trees, or to blow through and past them?  
>! Leaving all ease behind = remove 'e's, giving "wind" which could mean both meandering and blowing.  
  
I chased a husbandman's wife until she attacked me in her usual manner. I left, diminished, but I felt no loss.  
>! Husbandman's wives cut off tails ala 3 blind mice, so taking away 'd' gives "win" (no loss there).  
  
I made a teacher mad, and she tore my head off. This made me one of the popular kids.  
>! Taking off the 'w' gives "in" - being one of the "in crowd" means you're cool (or so they say).  
  
And now I am here before you, nearly unrecognizable—but a fraction of what I once was—but focus your sight just on my head. You'll see I was here all along.  
>! Looking at just the start of "in" gives you - surprise, surprise, "I" which was indeed here all along!