Happens to me too. Also can someone explain what the elemental crystals that are in the dungeons do? Also what does it mean when you go into a succubus trap and a person or crystal says something about your element or an element? That parts not really explained well.
The elemental crystals you collect as "Elemental Mana" (you see lower-left, as you collect them), which, when you get out of the Dungeon, is turned into Shards of the specific element. During a Dungeon run, you can only find Crystals of the elements of your currently-equipped Birthstones. Also, they use some of your MP each time you find them, much like the chest. The MP they each use starts at 10, but it is decreased if you upgrade the Birthstones (and those upgrades to the MP cost stack with one another, for all the Elemental Crystals).
Also, within the Succubus Trap, for each of those 2 events you mentioned (yea, it is not that well explained):
- For the Crystal. It will allow you to change one of your currently-collected "Elemental Mana" (aka. the ones you see lower-left, not the shards you cummulate over time in your inventory) into the Elemental Shard of the specific Crystal you see in that Succubus Trap (eg: If it is an Earth Crystal, and you choose to convert your 4/5 Water Mana, it will convert it directly into 4 Earth Shards). If you specify the same Elemental Mana as the Crystal of the Trap, it will simply convert that Mana immediately to Shards of that Element (much like how it would happen if you normally exited the dungeon; still useful if you're full on the Mana of that Element). If you choose an Elemental Mana that you currently have 0 of, it won't do anything (as there is nothing to convert).
- For the Succubus, I'm a bit confused on her general role, but roughly: she asks for Elemental Mana to upgrade one of your stats (this after you've had that Stat be drained by one of the Succubi Bosses), you would need to choose which Elemental Mana to give her for which Stat to upgrade (eg: giving Fire Elemental Mana upgrades Atk). If you have not lost any Stats to any Succubi, she won't do anything (thus, I currently do not know how much Elemental Mana she uses for how much points in the stats to recover).
You don't need to cum 4 times, but to end up in that situation 4 times. So you need to escape the position after it happens.
While I did consider still the game not needing 3 cums and that to be intended mechanic, there is yet another reason for there needing to be possible to still stay in-fight after 3 cums: The Status Debuffs. Namely, there being 3 distinct status effects for each number of cums (from 1 to 3). If you were to die on the 3rd cum, as currently stands (without my Mod), the 3rd Debuff, the one for the 3rd Cum, would remain unused, and quite useless (as it is applied right as you'd actually die). Judging as the Debuff further decreases your stats (but does not kill you outright itself), it does seem like it would make sense for it to have an effect, and thus, for you to live at least beyond the 3rd cum.
I'm not sure for the event triggers on their scenes, if you're theory is right, but at least for the reason that you'd die on the 3rd cum, as I checked in the game code, it did seem to be a slight misstype that was Pasted in each instance of 3rd cumming. It did seem similar with other similar Script calls (on losing HP on cumming), however this one immediately killing you instead of removing a part of your HP (and that's why I fixed it in the end).