No, your listing contract is for a limited amount of time. If you have only 1 month left, then you only need to continue using that real estate agent for a month. After the listing contract expires, you are free to chose whomever you wish.
Once the end date on that contract passes, you are free to list with any other agent of your choosing. If you are worried about the "temporary" status, don't be. I think your agent is just being extra cautious in case you change your mind.