The variables are getting overwritten, but not deleted.
At Touch Start, both Prev and Cur are set to the start of the touch cords.
As the swipe is ongoing, the Cur becomes Prev and, Touch cords become Cur every tick.
TouchFollowMe always traverses from self.X equal to the distance between Prev and Cur. This is the key to the implementation = Find the distance in between two touch coordinates within a tick and move TouchFollowMe by that distance.
Hope this helps.
Let me know if the implementation working in your project?