I don't know Luzifer all that well, Luzis, but I think he's given the impression of being the strong, powerful, intelligent, etc, type and here we are seeing the potential of a more romantic side to him. It's a side that, until you joined, he didn't show and of course since he didn't show it we didn't know of it. It's kind of like seeing the flip-side of a coin for the very first time and realizing that it's different then the side you saw before. :)
Just my half-asleep input on that though. Perhaps Alviss was referring to something else when he mentioned a new side of Luzifer showing.