If you leave the game on a cliffhanger "just because cool/edgy cliffhanger," sure. That's of course not why in this case. Players will understand why the chapter needed to end where it did when they play Ch5.
In regards to a cliffhanger in general. Sure, no problem, great.
A cliffhanger in a porn game is not the same though. I mean, these games are played for titillation.
Ending a release on a cliffhanger leaves the reader/player without an, err, "satisfactory conclusion" if you understand my drift. It ruins the, err, flow of their, err, appreciation for the story. Ruining their, err, moment, so to speak.
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Now, I've not played this game yet (lack of anal has pushed it down the list despite it looking and sounding very good) so perhaps this doesn't apply to this game but...yeah, not a fan of cliffhangers.
IMO, these games should always end with a larger than average (for the game) sex scene. This is for games that follow the large and planned story update schedule, rather than stop/start unplanned update schedule.
And, the warning that you are about to reach the end of content and that you should save should happen before that final scene.
This lets the player know that if they want to finish alongside the game they should do so now AND that when they load when they have the next update they get to play an erotic scene again as the first thing that they do.
Don't get me wrong, this isn't perfect of course. That last scene almost certainly isn't going to be able to please everyone (they want it with a specific character, or their kink isn't present in that final scene etc) but it is something.