I rented my home through a realtor and paid them a commission for finding the tenant. If I sell to the tenant would I have to pay the realtor some sort of commission from the sale?

Only if you have the house listed with this agent or agency. You should not have any more obligations to this agent or agency. So you are free to do what ever you like with your property as long as you do not have the preprty listed with them.

If the property is listed with them than yes you will have to pay a commission.

Good Luck