You can absolutely drink alcohol by yourself.

maybe not alcohol, but many of my closet friendships, which are probably the greatest sources of joy in my life (maybe romantic relationships come close), were formed around shared intoxication - weed, LSD, 2C-B, MDMA, Ketamine...

now obviously the relation has moved beyond that, we're very happy hanging out sober, and generally spend the vast majority of our time together sober, but getting intoxicated with someone is actually a good bonding mechanism.