It's clear that his romance arc is bugged at this point, I mean, why wouldn't it, you intentionally did everything you could to screw it up
. One would have to really try their best and meta game to get through his romance the way you did. What r the odds of anybody doing it that way unless you already know that the Necromancy book can tell him about the ritual? At no point in the game you'd know that the book contains the info for that specific ritual until you actually unlock the book at the vault in act 3.
You should sent a report to Larian about it, but I'm not sure they would even bother fixing it, the possibility of anyone going through his romance arc that way is remote.
