Let's tackle your question from two perspectives:
If your goal was to sell, did you HAVE TO sell, or would sell only if you GOT YOUR PRICE?
If the truth is you don't need to sell, personally, I would not have accepted the job of selling your property.
If you DO need to sell, then (just my opinoin), you'd be better off hiring a Realtor than selling it yourself (only if your goal is to maximize your profit.). I have answered numerious posts on Trulia so I am sure you can find interesting reading.
Just to summarize, studies consistently show that owers that sell by themselves sell at about 16% lower than a Realtor. Also, if 90% of the time the buyer first sees the home they buy with a REALTOR, why would you exclude 90% of the market by marketing it yourself (notice I didin't say "sell" because over 85% of home owners eventually list with a Realtor when they do sell.
Lastly, the first poster is correct. Read your contract. If the Realtor submitted a list of brokers that have contacted him about the property (and buyers), there is usually a "protection period". If any of the brokers or their buyers contacted the Realtor, and he submits the list to you, you would be obligated to pay a commission to him (per the contract). Sometimes Realtors do not submit a list.