i don't want to get all academic here or in any way diminish what you are feeling. but there are some fascinating theories out there about our emotions and what actually drives them.
Fear itself is not an instinct, it is a learned behavior/emotion. we learn from others over time HOW to react in certain situations. and make choices in how we feel about those situations.
for example, you put ME up on the 10 meter dive platform and there is no way, no how, i'm jumping off into the water. however a professional diver who has been trained believe in their skills to not let them die on impact, does not hold that same fear.
the sad experience of your BIL's death, followed by your AH's chosen response - to DRINK - has "taught" you to fear not only the outcome of the drinking, but what you see as the catalyst for that.
when in reality, your AH can and has drank on MANY other days, for a multitude of other excuses....um, i mean, reasons.
you could have the same fear over Tuesdays, football, weather forecasts, or a missed newspaper delivery.
as we unpeel the layers, we can ask ourselves - is it really even the drinking that is MY problem, my FEAR.............or the choices i might have to make in response????