Be careful at this point. You have gone quite a way down the road with this realtor and the rules that are in place for agents may be costly for you.
First, the agent is entitled to a commission for the sale of this property regardless of whether or not you choose to have them finish the transaction. The rules of the MLS and the representation agreement will outline this for you.
In the end you may want to heed Aaron and Susan's advice and try to work it out with your current agent. The closing table will heel most all wounds.
Have a heart-to-heart with your agent and/or the broker as to your concerns. Everyone else below is right about the listing contract... that stays in place regardless.