[Because Nick's a detective, and it's sort of his job to figure things out?

Nick stays silent while Monroe explains, even when he rambles a bit, because it's pretty obvious that this isn't something Monroe's comfortable talking about, and he doesn't want to say anything that makes it worse.

Or that makes him stop explaining, because this is something Nick really needs to know about.]

It's fine, man. I don't exactly know how it works, or anything, but you know I trust you.

[That's probably not enough, is it? Nick should say more, he can tell Monroe's freaking out a little. He shrugs slightly.]

We always have each others' backs, right? As far as I'm concerned, you're the closest thing to family I have. So no, I don't think it's bad.