Your cranks are fine. Your BB spindle is also fine.

You can ruin a set of crank arms if you ride them when they're loose but often it doesn't happen so quickly. As long as you catch the within a few dozen miles of being loose and don't mash up any hills you'll generally be alright. Next time you install them make sure all mating surfaces are free of lubrication, grease the crank bolts and use proper torque and they won't come loose unless something is wrong.

Buy a torque wrench. Read this. And hate the player not the game, son.