The priest is all but radiating a patronising sort of concern for his feelings, and while it should by all accounts annoy the shit out of Zach, he can't help but crack a bit of a smile at the familiarity of it. Annoying as it is, he can't help but be endeared by the sheer persistence of the man in the help he wants to offer his 'little one's'. There's probably quite a few humans that are genuinely honest in their motives, but Zach usually doesn't have the pleasure of meeting them. Not to say that he doesn't enjoy the more sinful and depraved side of humans- on the contrary! It's just interesting in it's novelty, if nothing else.

"Yes priest, you are very caring and selfless and all that shit- no need to convince me even further." He rolls his eyes and helps the priest get his arm in his sleeve with a care that belies his words. 

"You probably believe what you say too, all you religious types seem to do. But don't think I didn't notice you being all... stiff and weird after tonight. I don't know if you guessed or if you talked to someone, but I know what you 'good' book says about... people like me. You don't have to force yourself to be all forgiving and shit if you're just going to be weird about it later." He makes sure to inject just enough covered-up hurt to make it all the more tantalising for the priest to want to break his wall down again. 

Of course the man has no idea what he's talking about. He is pretty sure Kiel hasn't figured out yet that Zack had cheerfully slept his way through an impressive list of guys in the months before he ended up on the priest's doorstep. And if he wasn't going to figure it out on his own, Zach would have to tell him himself. And what better way than to pretend to assume he already knew?