Huge problem - what do I do in this situation? NYC

[Steve Candor]

I'm the landlord and I rent an apartment out. Someone left a security deposit and we signed that she owes the first months rent on move-in date. We agreed on the date and the address of the apartment.

Now two days after the open house and after I tell everyone else they can not have the apartment - tenant calls and says that I have to return her security deposit because her boyfriend got another place.

We are in New York City. The problem is that I am no longer in the city and specifically came to rent out the unit.

In our lease it does not say refundable or non-refundable. Only security deposit. She says since it didn't say refundable I am required to give it back. 

Anyone know what to do? 

[Dawn Anastasi]

I've switched to taking a "holding fee" which will hold the unit until they move in. The holding fee will become the security deposit upon move in.  If they do not take occupancy by the move in date, then the holding fee is forfeited.

I also only do month to month rental agreements with 30 day move out notices.