Are all scenes available in one save or does getting one lock another?
Viewing post in Eternum: Colored Walkthrough comments
In the scope of entire lewd scenes, yes, you can see every lewd scene in just a single playthrough. The walkthrough calls this the "ideal route".
In the scope of the individual animations that make up a full lewd scene, there are a few mutually exclusive ones, though this should be obvious while playing.