Whether your real estate agent is due any money comes down to WHY the contract fell through.
Your Buyer Agency Agreement should state when your real estate agent is due money. Many times it states when the house settles, but sometimes there is a clause that if the agent has done what they can to get the deal to closing, but the buyer has defaulted in some way, they may be due compensation.
If your agreement is the first, then then agent should not be due anything. If the second, then he may be, depending on why the contract fell through.
That being said, if they agent is saying he is due compensation and you disagree, you need to speak with an attorney.
If you have further questions, please let me know.
Keller Williams Excellence Realty