It might help me.

It might make things clearer.

It might help to justify myself in my own eyes.

Not that I have any doubts, of course (about leaving Jerry, I mean), but that when I saw it in black and white I could be even more convinced that I was doing what was best for him and best for me.
So I brought the manuscript down to my own room, and this evening I have commenced to write.

I can't finish it to-night, of course.