Is it safe to leave pork loin out over night cool it again and then cook it?

No, that is very dangerous, and why would you want to leave it out anyway? You will just encourage bacteria to grow. If you are defrosting it from frozen you should do so in a fridge, allowing sufficient time for it to defrost fully. If not, keep it in your fridge overnight anyway at less than 8 Celsius, then remove it when you wish to cook it.