How to achieve diagonal movement opposite to current diagonal movement?

Hey guys I’m a beginner so i want some help. I want my character to be moving in a diagonal direction from the beginning and when i click my mouse i want the character to move in the opposite direction diagonally and when i let go of the mousebutton i want the character to move as it was moving before diagonally. Right now i did some basic coding but i cant get it right.
I saw @robertbu give some solution for diagonal movement problem so i would really like some guidance.

Diagonal (as opposed to orthogonal) movement is just moving on multiple axis at the same time

i.e

Vector2(0, 1); is an upward movement where as Vector2(1, 1) is up and right.

and the inverse direction would just be
-Vector2(1, 1) or Vector2(-1, -1)