He has been glad for the partner he'd gotten, someone that he found he trusted in ways that Nik never had trusted anyone else. Now they're talking like this and he realizes he needs to do something he hadn't ever thought he would.

Be fully honest.

"So... look. If we're talking like this and about how much I trust you, which I do? You should know something. You met Elijah, right? When we were first teamed up? Yeah, he's my older brother. How they found me to bring me in."