In Fahrenheit 451, how does Montag feel after he discovers that Clarisse has dies, and where is it found in the book?

In the book, Montag finds out that Clarisse is dead when
Beatty comes to his house and tells him.  Go to that part, then look at what Montag
thinks and says after Beatty leaves the house.  You can tell from those things that he
is deeply saddened by Clarisse dying.

Montag shows his
feelings about Clarisse's death through what he thinks.  First, he thinks about what
Clarisse said to him.  He thinks about how she talked to him about her family and how
they liked to talk.  Montag thinks about this and about how different that was from what
is normal in their society.  Second, he thinks about how he liked Clarisse so much
better than he liked his firefighter colleagues.

So he is
clearly saddened and he is thinking about how he dislikes the society he lives in.  He
is coming around to Clarisse's way of thinking.