There's another possibility that you haven't mentioned, per se, while we're getting into making oneself out to be safe.

He's mentioning needing "one more night" with his brother and asking us to abstain. Why do you think that might be? After all, if one or both of them is a demon, there's only one thing they can be doing at night that's that important.

What if our Incubus is soulbonded?