My heart stopped when I read the first paragraph of your post. It only started again when I saw that Drake was alright and out of danger. What a scary thing to happen!!! But, like everybody else said: don't blame yourself. You only wanted to give him a good time, and you're right, it could have been much worse if he hadn't sliped out of his collar
Give him many hugs from us, with best wishes for a quick recovery from his wounds.