How to deal with a US fianc� visa if the relationship ends?

With the fianc� visa, I am 100% responsible for my partner once he arrives in the US until we get married and he becomes a legal resident. However, the relationship is not going well I don't believe we wil get married within the three month window. I know I am able to null the visa, but what if we just go out separate ways and he stays out the remainder of the visa with family. Could I be held accountable for failing to provide a home, food, etc. for him even though we are broken up and have no intention of getting married? And can he bring a case against me?