how will Montag's changes affect Mildred?

To understand Montag's reaction it is important to note his meeting with Clarisse. Clarisse had asked, "Are you happy?" and he was startled, and started to think that perhaps he wasn't. Meeting Clarisse had really upset his normal way of thinking; he was left feeling unsettled, questioning his happiness, and wondering why he all of a sudden felt old and tired. Her mere presence was so refreshing and alive, that he felt his own life drab and empty in comparison.

When he finds Millie, first of all, he is not surprised:

"An instant before his foot hit the object on the floor he knew he would hit such an object."

He was not surprised to find her empty pill bottle. This indicates that he is, at some level, aware of Mildred's unhappiness, and a suicide attempt is not a surprising thing for him. But still, as he realizes what has happened, Bradbury describes his feelings more symbolically through the jet bombers that scream over the city. Montag can't exist with Mildred, she is the symbol of everything he loathes. Consequently Mildred is driven to self destruction. Her vapid life and her husband'd indignation drives her, eventually, to kill herself.

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