[Shikijin]

Spoiler for Comparison to the novel:

In the first (actually, second) chapter of the Nise Araragi, when describing Senjougahara, mentions that she suffered a trauma and that's why she came to be like that. The point is that Senjougahara wanted to change and Araragi was feeling like he was helping her change. That's why he puts up with what she does. He's not M. One could think Senjougahara was the ideal girl for him because Araragi liked to help and Senjougahara needed help for a long time. Anyway, as the LN obviously don't describe Araragi's feelings in detail, many other interpretations are also possible.