I am not really good in physics so let me recapitulate what you said to the best of my abilities. You said that the drag force shouldn't be a constant then does that mean that the ball will only come to a halt when:
-vx = 0 and vy=0 but also when the force 'a' which initially had a value of 0.1  [double a = 0.1] gets its value reduced and reaches 0.0 at the same time that vx and vy get the value of 0?

Is there a formula to be used to gradually reduce the speed of a ball in motion and then stop the ball at a certain point and time?