I agree given that in stories that tend to have saintesses, he probably was trying to kidnap the saintess to revive his dead wife.
That's what I thought too
Or maybe, it was the temple and saintess who orchestrated this. Grace was drinking something she dont know before the possession. And it was from the temple. That pill might be something that triggers hallucinations of some sort. Else she's really schizophrenic. Or both. Then when she died, they switched their eyes on the duke. Grace said said that in the original novel, the duke gave that precious cloak to aria. Maybe after grace died, the temple made it so that he sees aria as grace. Making him possessive of her. Also, that aria seems shady. Her gaze. I mean. When grace saw her hubby and aria on her way from the workshop.
I dont know. This is just my thought. I wish it gets updated more often.
I have this feeling that the ml she read in the novel before she possessed the fl spiraled coz the fl died. Remember his dying words? I feel like he was talking about his wife. Like it broke him when she died. Imo, novels tend to flag males around the fl a male lead even if they're really not. Just to make it look like the fl is so lovable.(〜￣△￣)〜