You can call her by her name directly. If you mean how do you refer to her, there is no special term, just as you said it in the question. She's your girlfriend's sister.
If they were to get married then she would be your sister-in-law.
to flatter and maybe oneday go out with them And they probally like you as a girlfriend, or as a sister.
You can be friends with siblings, but the term you use depends on what you prefer. When a male uses the term "girlfriend," he usually means a female with which he has a romantic relationship. Most people would call their sister simply, "my sister."
If you are attracted to your girlfriend's sister, you need to be very careful. You need to break up with your girlfriend because she finds out and they will both hate you.
I don't think he has a girlfriend but he DOES have a sister
get very jealous and hurt my sister if i see her kiss my girlfriend. sex them up
jasmine was his sister
pit bulls girlfriend is my friends sister
No, he doesn't have girlfriend. He have only sister....
A girl might say: Hey girlfriend! or: whats up sister?
Men fantasize, yes, but when it's about your girlfriend's younger sister, then there is seriously something wrong in your relationship.
he doesnt have a girlfriend but he would call her shawty