You're talking about 2 different things:
Adverse yaw:
Upgoing aileron produces less drag than downgoing one (more lift = more drag, less lift =less drag). Therefore aeroplane will tend to yaw away from the direction of roll. The competent pilot will prevent this by use of co-ordinated rudder with aileron.
Some aircraft have differential ailerons (they go up further than they go down), and /or frise ailerons (the upgoing one protrudes below the wing as well, creating extra drag to lessen the adverse yaw). Both of these techniques spoil the roll performance of the aeroplane, so older types without theses aids and with consequently better handling are much nicer to fly, but demand correct use of rudder to counteract adverse yaw.
Try this in a Chipmunk: Pick a point on the horizon, and roll the aeroplane rapidly left-right-left-right without use of rudder. Notice the chosen point occilate left - right-left of the nose as you do so and the adverse yaw takes effect. Now do the same thing but using co-ordinated rudder with aileron. the aeroplane will roll more crisply, and more importantly the roll will be axial with no yaw - the chosen point will be nailed to the spinner.
Spiral stability:
Piloted aircraft are spirally unstable. that is, if a wing drops the aeroplane will slip toward the dropped wing, the nose will drop, and the speed will increase. If the pilot does nothing about this, it will develop into a spiral dive with a very nose-low very steep spiral and the speed building until it exceeds Vne and soemthing (usually the tailplane, followed imediately by the wing) breaks.
Free-flight model aeroplanes are designed to be spirally stable. By use of large dihedral angles, the aeroplane has so much roll stability that a wing drop will be self-corrected, and a spiral will not develop. Early WW1 aeroplanes were often sprally stable, which explains how they could fly in IMC without use of gyro instruments.