If you try the Minrathous route, you find out that Lucanis actually cares about Spite very deeply. Something I don't think we get deep enough into during the Treviso route. If you save Minrathous, you don't get the conversation in Café Pietra after saving Caterina and dealing with Illario. Instead, Lucanis has a dialogue with Rook at the fireplace in the Lighthouse.
Lucanis starts the conversation saying,
I've been thinking. Treviso is as safe as we can make it. So when my contract to you is fulfilled, Spite and I will go our separate ways. Literally. I'm going to seek out a way to separate us, wherever that takes me.
Which may initially sound as though he just wants to get rid of Spite no matter what.
The dialogue goes some fascinating places...
Rook: And what about the other person in this equation? How does he feel about it?
Lucanis: He dreams of freedom. I've... shared those dreams. He never chose this, Rook. Something must change.
Rook: If you can manage it, that's a good idea.
Lucanis: It's the only answer. For both of us, and for my family's safety.
Rook: So why don't you sound happier about it?
Lucanis: Being possessed... It's not like separating oil and water. Each element permanently infuses the other. Spite wears my face. Uses my skills. I know I've grown stronger, so... Say I cast out Spite, with all he's learned from me. What then? What if I free myself, but unleash a true Demon of Vyrantium?
First of all, I think it's interesting that not only can Lucanis use Spite's abilities to empower himself, he himself seems to have grown physically stronger from their connection, as well. He talks about it as though it's something that could last without their connection, too.
Second of all, he definitely sympathizes with Spite and has very mixed feelings about the idea of their separation.
Rook can be either reassuring and/or doubtful about it.
Rook: A demon who's worked in a team, saved people and made friends.
Lucanis: He'd lose them if I cast him out.
Rook: You keep saying that... like you'd miss him.
Lucanis: He's been part of me. He'd be alone.
Rook: Spite will only be alone if he chooses to be. But you can't control that.
Rook: You sound like you've still got some doubts. For all you know, Spite comes out with your knack for vanilla-and-nutmeg tarts.
Lucanis: Rook.
Rook: My point is, you don't know what will happen.
Lucanis: I know that Spite - a part of me - would be alone.
Rook: Spite will only be alone if he chooses to be. But you can't control that.
Rook: If it came to that, you could handle him. Or are you worried you wouldn't be able to put him down?
Lucanis: I worry that I'd... miss him.
Rook: If Spite gets his freedom, it's his choice what to do with it.
The conversation continues:
Rook: All you can do is trust that you're making the right call. For both of you.
Lucanis: (sighs) I know. But from someone else, it's easier to believe.
Hardened or not, Lucanis cares about Spite. He cares about him a lot. He thinks about him with compassion and a great deal of sympathy. He's so concerned about the possibility of abandoning him, leaving him alone, making him experience loneliness. Not only that, he thinks he would miss Spite, as well. What a beautiful development from how we first meet them.
