Hints in dialogue

His jealousy manifests in small ways:

• Subtle emphasis when addressing solfrey lovers as "my lady" - both yearning and bitter
• Tendency to work late when MC has visitors, torturing himself with distant sounds

An early sex scene

You see him watching you have sex with a disgusted expression on his face.

MC: What are you doing making that expression. Jealous?

Sunwei: Scoffs Did becoming a necromancer make you a bad mind-reader as well?

MC: No, just... using my empathy. You wanna have a go at these slaves after?

Sunwei: To go after you, with a dirty used up slave girl? And be compared to my lord who I could never hope match up to? No, please spare me. I still find within myself a romantic streak, I want to be in love when I have sex.

MC: You'd rather I help you find a romance with a commoner girl?

Sunwei: Having my lord pick my mate, I can't imagine a more violating one could do to a human being... Oh wait, having my soul enslaved by necromancy magecraft, huh.

He sees you raise your eyebrows at him.

Sunwei: Oh don't worry my lord, I understand you had no choice, it was too dangerous to let it be otherwise. I trust your decision completely and I approve with no reservation. My enslaved soul ensures that.

Second time

MC: You should find yourself a girl. I'm sure there are plenty who'd be interested in a scholar...

Sunwei: bitter laugh I see how they look at you, my lord. Anything else would be... settling.