It bit you because no matter what you think about your relationship with your BP, your BP does not like you. It may tolerate you, but it by no means likes you. If you understand snake behavior you got bit for one of 2 reasons;1. it thought you were food and/or 2.it was scared of you and felt threatened. Either is acceptable and understandable.
The best outcome for taming a snake is not that it will like you, it's that it will tolerate you enough not to continue to bite you.

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