Question about my alcohol consumption

I am 21, almost 22 and I am 5’11, 125lb. I don’t typically drink consistently but when I do, I tend to go overboard. The other day I bought myself a 750ml bottle of Gentleman Jack and finished the entire bottle by myself in one night. My primary question is, how damaging could this have been at my BMI? My other question is, how the fuck am I able to do this without getting sick, and should I seek help?