So, I came out to my best friend, the person I probably hang out with the most. His reaction was... better than expected, but worse than I hoped. Basically, he promised to support me no matter what (yay!) but asked a ton of questions about whether I was sure and whether I realized how I might end up as some ugly half man, half woman creature. Fortunately, some time explaining how I've thought about it extensively and would rather take the risk of not passing than continuing to live in a body I'm uncomfortable with, seems to have convinced him that this is happening.
I know he's having trouble with this, so I'm hoping he'll be okay in time.