Is my lease binding yet?

Yep, he keeps the $325 and you walk away. Make sure you let him know right away that you are not taking the apt. He cannot charge you rent as you did not even activate the lease yet. Your term does not start until Aug 16th. Its not your apt until then and you dont want it. Kiss the $325 goodbye and next time make sure that you actually want something before putting down a deposit. The damages to the owner is he took it off the market to other potential tenants, stopped advertising and has the costs from the month you are not there. Its a non refundable holding fee for changing your mind and is commonly used.