Billie is complicated. Lucifer kinda had to know, and Billie hated being treated.like a freak in hell, so she begged Alex not to tell. I think it's going to be kinda cute how she tells him to. Because she isn't as confident as she seems so she is going to actually be shy about it. 

And yes dear, I couldn't help the brain puke. Warning, it gets a little heavy.

Edit: when we finally do the change, I'm thinking [url=http://03.wir.skyrock.net/wir/v1/resize/?c=isi&im=%2F3050%2F78843050%2Fpics%2F3039592819_2_3_gdI6eAAS.jpg&w=552]this[/url] is.going to be Billie.