From Twitter:
The bartender at Johnny's S & P's Bar on Greenwich Street is a ① mate of mine. He often gets me my drinks ② on the house.

A. The meaning of ① is:
spouse
acquaintance
buddy
co-worker on a ship

B. The meaning of ② is:
inside
on the second floor
on the roof
free
at a discount

Answers And Explanation :
A. ① mate means buddy (or close friend), and is used in other English-speaking countries beyond the US
B. ② on the house means free