"My g" is just a term that a close friend would call another close friend.

What is the real meaning of G?

A G is a unit of measurement of the force resulting from acceleration. One G is equivalent to the force of the earth's gravitational pull.

What is Gee slang for?

gee. noun. Definition of gee (Entry 2 of 3) 1 : the letter g. 2 [grand] slang : a thousand dollars.