When your partner is pulled wide, the shape of your team changes immediately. If you stay in your original position, a large gap appears through the middle of the court.
Your job is to react to your partner's movement and cover the space they can no longer protect.
What to do
Slide toward the middle while staying at roughly the same depth. You are not abandoning your own side; you are temporarily making the pair compact again while your partner deals with the wide ball.
This movement also prepares you for the next shot. If the opponents attack the open centre, you are already closer to the space that matters.
Why it works
After the ball has been played, recover together. Pair movement is continuous: one player is pulled out, the other covers, then both players rebuild their normal shape.
The useful cue is simple: partner goes wide, you protect the middle.