what happened to clarisse? Why didn't Mildred tell montag this information right away?what affect did all of this have on montag?

When Montag is asking his wife about Clarisse, Mildred says quite casually that she is pretty sure Clarisse is dead. She says that a car hit her four days ago but simply forgot to tell him. Montag is of course crushed. Clarisse was the person that ignited him back to life.