What excuse does holden give for not committing suicide by jumping out the window?

Holden goes to Central Park in New York City, and sits by the frozen pond where, in the Spring, the ducks would be swimming. He is despondent, having left the hotel because of his confrontation with Maurice. He sits there thinking that he could get pneumonia and die.

He starts to think about his death and his funeral, who would attend, then he remembers that his mother is still mourning the loss of her son, Allie. The thought of his sister Phoebe being sad at his death is what stops Holden from staying in the park and freezing to death.

It is his love for his sister that keeps Holden from committing suicide