Final answer:
The phrase hints at a change in dynamics between two individuals if one finds a new romantic partner, reflecting a common narrative theme about how new relationships can test existing bonds.
Step-by-step explanation:
The phrase "Until you get a girl of your own" implies that the speaker anticipates a change in the relationship or interaction between the two individuals if one of them were to enter into a romantic relationship with someone else. In the context provided, this might suggest that the current dynamics of their friendship or relationship could shift if either party finds someone new to be romantically involved with. It reflects a common theme in narratives where existing bonds are tested by new affections.