Being sued by my ex, please help

What is the name of your state? (NH) My boyfriend moved out of our townhouse shortly after we moved in. He sent a letter to the property management co. stating he wanted his half of the security deposit back (675$) when I move out. I sent a letter of agreement to them shortly after. The PM stated in writing to me that they would not be giving the deposit back to him until I move out anyways, unless we came up with a agreement that I would pay him his money myself, then he would be taken off the deposit totally.Well, now its 1 1/2 yrs later and hes demanding his money, not wanting to wait for me to move, wanting to scrap our agreement we had. I do not want to give it to him until I move. What are my chances of winning if he takes me to court? Can I sue him back for my legal fees if he loses?