Possibly, but I somehow doubt that it's related to dating anyone in particular.
I know I tried to date Val (worst girl, don't @ me) but that didn't work. I haven't tried doing it when dating Sarah, though. Maybe she works?
But then girls can't get the Heroic ending!!! You can only date Sarah as a dude. But I don't see how that would do anything. Is it a certain party combination? Because you can only unlock Ashley's berserker spell with her and Julia in the party on floor 21. Is that plotline resolved after Ashley defeats that queen lady? Are those girls ever mentioned again? If not that feels like a bit of a plot hole.
Also, if anyone was wondering about the Molly quitting storyline, you gotta date her, get her third date at the lake, say she works too much and keep pressing, go to the store and talk to the dude, go back to the lake, and when you get the option, you use the persuasion spell. I dunno if that progresses her romance at all since you don't get the CG, but she quits her job. Buying stuff still makes it seem like she's there and not the dude.
Once you defeat the Monster Queen, one of two routes plays out:
One ends it with the Monster Queen's death, the other one involves you capturing her and thus being able to play with her in the Monster Ranch. As far as I know, that route is considered complete.
The girls aren't mentioned again, AFAIK. Which, to be fair, doesn't surprise me - this game has a lot of plot holes as is.
I highly doubt that there's a certain party combination being required to get to the Heroic Ending but hey, if someone knows, you're more than welcome to correct me!
Also, I heard from a friend who's a Patron that Julia is gonna be possible to marry on the Heroic route now, but I don't know if it's true or not.
Monster Queen (IIRC, she's called the Frost Queen or something?)
She's the antagonist of the Intelligent Monster's route, which is insanely stupid to access.
To access it:
-You must have Julia
-Julia must have Detect IIRC (1200 Support proficiency - yes, you read that right. Have fun...)
-Julia must be in her Normal Personality
-Julia must be part of your active party (meaning you bring her to the dungeon).
-IIRC, you must have obtained the Berserk spell for Ashley (level her a LOT - try being level 25-30 at minimum).
Lose 2 battles against any 2 random mobs that don't give a unique ending (for example, Baby Slimes).
Lose 2 battles against 2 Monster Girls (Flower Girls, Slime Girls etc).
Enter the dungeon with a party consisting of the Protagonist, Julia and a third member who is not offensive (so you can't bring Val, Sarah or Derrick for example - Cass or Molly is fair game to bring).
Wait around and see a scene in which Julia notices monsters following you. Choose either option.
I forgot how long it's after that, but I think it's 3 more scenes (I could be wrong on this), a boss fight will occur... during which you only have access to Ashley. Who you can't control. Because she's permanently in her Berserk state. Which is why I told you to level her a ton.
There's four possible outcomes:
-You lose: game over.
-You lose: Julia has her gun from the Julia's Arsenal route. Julia shoots the Frost Queen and saves the day. It does not matter if Julia got help from Brittany or not.
-You win: Frost Queen gets her neck broken by Ashley (automatic if you win).
-You win: Frost Queen gets enslaved by you (there's like 3 lines total where you can cast a Chakram on the Frost Queen after realizing she's pretending to be dead). This unlocks her in the Monster Ranch for your amusement.