Why does Behrman likely accompany Sue up to her studio?

So either he could see how big he needs to paint, wants to see her, or wants to tell her thats she's not gonna die

“You know that I love you, and you led me to believe, Miss Fairfax, that you were not absolutely indifferent to me.”

The phrase "not absolutely indifferent" is an understatement. An understatement is a rhetorical device that contains a phrase of lesser strength than what would normally be expected. Understatement is used for emphasis and irony. In this case, the speaker wants to express that Miss Fairfax loves him, or at least is fond of him. Therefore, describing this as "not absolutely indifferent" is an understatement.