This got me wondering. Since Alastor and Lucifer are a couple, does Lucifer ever get upset when Alastor talks or thinks about Vox when it seems he's in a sad mood.
I know Alastor doesn't like anyone talking about Vox around him, but it seem to me he still has Vox on his mind every once in a while when it seems he sad.
Lucifer is not upset with Alastor, Buuuuut he is upset at Vox and the circumstances. He knows Alastor still thinks about Vox, but he also knows from when Alastor lets himself talk about it that it's not Al looking back on these memories fondly.
Alastor is grieving the loss of his security blanket. He really, truly relied on Vox as a way to explain and justify why his mother would be in hell. Alastor, prior to S2 Finale, really needed to believe good people could be sent to hell. And Vox was just his delusion to base that faith on.
And its very well known to others NOW that Al HATES Vox. HATES. Attack-on-sight type aggression.
So, Lucifer isn't threatened or anything like that. But he is sad that Alastor's deep belief in goodness, the thing that helped him connect with Charlie and see the beauty in hell (helped Lucifer feel proud of what he's built) was shattered.