Do I understand the usage of "girl" & "boy" correctly?
"Girl/boy" can mean friend or girlfriend/boyfriend depending on who uses it.
e.g. Mike is my boy. (If a boy says this, it means male friend, but if a girl says this, it means boyfriend.)
e.g. Jane is my girl. (If a boy says this, it means girlfriend, but if a girl says this, it means female friend.)

It can also mean sidechicks / sideboys
e.g. Katie is one of Jack's girls. (Jack has many sidechicks)

Do I understand correctly?

Thank you.

Question

Do I understand the usage of "girl" & "boy" correctly?
"Girl/boy" can mean friend or girlfriend/boyfriend depending on who uses it.
e.g. Mike is my boy. (If a boy says this, it means male friend, but if a girl says this, it means boyfriend.)
e.g. Jane is my girl.  (If a boy says this, it means girlfriend, but if a girl says this, it means female friend.)

It can also mean sidechicks / sideboys
e.g. Katie is one of Jack's girls. (Jack has many sidechicks)

Do I understand correctly?

Thank you.

Answer

I think you are correct in your meanings although I have never seen the words"sidechicks or sidegirls".  We would say "girls on the side or boys on the side"

Answer

My boy/girl can also mean son/daughter.

It also depends on the context.  If you say "my man/girl" it could just mean a friend, co-worked or an acquaintance did something positive like got tickets for you and a group of friends for free you could say  "my man/girl" as in you are the man/woman  for being able to do this.  But in America (and Canada) beware, any use of gender to the wrong people can get you in trouble!