bidirectional DC motor with DPDT

tekstyle

I found some N20 geared DC motor that I plan on using as a switch. based on this link, it mentioned the need for a flyback diode: https://forum.duet3d.com/topic/6415/bi-directional-dc-motor-control-without-h-bridge/1

does the diode go between the contacts of the relay coil? or the DC motor?
if it goes between the DC motor terminals, which way does the stripe face? I am confused because if I have it one 1 way, wont reversing the polarity create a short?
I plan to use a fan output to power the DC motor. would I need another fan output to control the relay?

I don't want to use the PWM output or the heater channels because they are used for something else. the only output channels I can think of that remains are the fan output to perform this function.

thank you.