[This time Leo does hit Niles's door, but it's gentle and mostly out of frustration]

If I even attempt to tell you, something terrible and irrevocable will happen and I will not put you through that. I could not live with myself if I hurt you that way, Niles.

[He can hardly live himself now, knowing how Niles died for him]

But I can and will find you something to show that I mean you no harm. I promise, Niles.