will it be possible to have sex with oriana later in the game?
Let me save you some time and answer in general. If the character has a name input (where you decide their name) that is what I consider the main cast character(s). Main cast stays with you all the time and is also considered Li (love interest) later on in the game (should you choose it). It's just that it takes a little or a lot longer in order to get there with the main cast. So, yes. Lilith is also on the list. Just not right away kind of thing.