This doesn't make any sense to me.
By definition a cuck or cuckold is
So if we have a dude and a girl and a third chad guy.
If the dude is married with the girl, and she goes with the chad --> The dude is definitely a cuck.
If the dude is in an exclusive relationship with the girl, and the girl goes with the chad --> Also cuck.
If the dude is dating the girl (non exclusively), and she goes with the chad --> He's not a cuck. She's not his girl.
If the dude is in a situation-ship with the girl (again non exclusive), and she goes with the chad --> Again not a cuck.
If the dude has a crush on the girl (no relationship), and she goes with the chad --> This is just sad. It's not his girl.
If the dude sees a dream with the girl, and she goes with the chad --> He has to change the sheets.
In order for someone to be a cuck, he needs to be in an exclusive relationship. Otherwise it wouldn't make any sense.