All honesty, it doesn't sound like psychiatric illness (which, as far as I'm aware, means there is the possibility of a cure, however slim), but more something incurable eg psychopathy/sociopathy, which means no moral compass, or empathy. These fuckers are capable of doing anything, if they think they will get away with it.
As regards what he was using, the chemical taste sort of makes me think possibly 1,4-butanediol (1,4 BDO), as it and GHB are rapidly metabolized to standard sugar breakdown compounds (ie become part of the citric acid cycle), with no telltale metabolites (any benzo would leave something detectable for a good few hours).
Not wishing to cause alarm, but he could have killed you, without a trace of foul play. Twats like him are the reason so many women have utter mistrust of men...
