No, in most states, but you aren't going to get a lot of sympathy if you try to enforce your contract. It usually depends on the specifics of the situation. The fact you are asking suggests that you are new at this. New investors often use poorly written contracts. A contract could have holes that let him out.
Why is the seller backing out?
It's usually better to simply walk away. Even if the seller is forced to keep the agreement. He can make life miserable for you. He probably will never be available to show it to your end buyer. He will not get documents to you that are needed to close. He probably will not communicate with the closing attorney/title company. The list goes on and on.
Tell them up front what your intentions are and what you're going to do. You'll also feel better.