Started talking to a Nigerian on dating app and we v/c everyday on what's app. Could he be approved for temp visa until I go over there soon?

The only way that you can sponsor him is for a fiancée visa, but in order to do that you have to physically have met him within two years from the filing of that application. Alternatively, he could always make an appointment with the consulate in Africa, and apply for a visitor visa, but you would not need to sponsor him for that. He would have to qualify independently.