i think i remember seeing something about this current version bein a complete version [unless the devs said otherwise and i missed it].
i encountered that too at first. I wanna say it either fixed itself on a reinstall OR fixed itself after progressing to ashton plains.
but regardless there should be sex gameplay when you submit to the monster [as all combat encounters do].
there is also after you defeat final boss the ability to go to a tentacle cave for other scenes if thats what you meant instead.