Just caught this thread, and I hope your little Bill continues to do well. As a fairly new snake owner, I am also paranoid. If an accident like that can happen to someone who has the experience and commitment to your animals that you do, it can happen to any of us.
The funny thing is that, before I went to the herp show to get my first corn snakes, I actually went to a local pet store to 'test handle' a hatchling! I was terrified that I would either grab it too hard, or let the little thing slither right out of my hand and fall to the floor! I passed the test, and was so captivated by the one little hatchling that insisted on crawling back up my arm when I went to put him back, that I bought him, over-priced little amel that he was. He's still probably my favorite, friendliest snake.
You're one of my heros, so keep your head up. Things just happen sometimes.