i do get why the situation "seemed" to have no other options. dude's birthday, the sick wife, the expensive cognac, the familial bonds.
however, if it was peanuts he was handing out and you were allergic, you would NOT have done so just to comply, fit in or not make waves.
you've been around long enough to have some experience at saying NO. no thank you. i'll pass. i decline. oh shoot look at the time, gotta run.
so you made your choice.
your CHOICE.
to drink. regardless of how nasty, or the why's of it, in a sober frame of mind you chose to drink again. it was not inadvertent. it was vertent. DELIBERATE.
never heard of pure or unpure sobriety before. it either IS or it is not. like pregnancy. anything else is PURE rationalization.