I honestly don't know.
Half the time it seems like the relationship/lust levels don't matter, whilst other times they do.
Oh, I got the one in the infirmary. If Evil Darcy finds you in the infirmary, you try to run away and she grabs you (which I think is ALSO random) first she fucks you alone, then Anita finds you there, and she joins in.
I thought that the "you try to run away, but Evil Darcy catches you" scenes were all bugged, because in both the Café and the Gym scenes I always got the same scenario.
I mean, both scenes in the Café were exactly the same to me (you surrender to her, or you try to run away and she catches you), she punished MC for running away in both scenarios.
While in the gym, it was also the same scene, but switched: she mentions 'you should've tried to run away', and punishes you only once, if either you surrender to her, or if she catches you trying to running away.
In the infirmary instead, if you surrender, she only fucks you once, no Anita. Then, only if Darcy catches you running away, that's when Anita comes into play.
Thanks to that, I realized that maybe the other rooms with Dark Darcy also had two different, not bugged, scenarios, and I was right: I also triggered the "failed to run away from Darcy" in both her room and her work room, and there was a punishment scene in both rooms.
Finally, I think that Tina won't fuck you anymore in the gym if you agree to follow Montanna in her dungeon, because she never attempted anything with MC after that...
So I think that, unfortunately, all her scenes in the gym, threesome scene with Anita included, is forever lost if you accept to go in the dungeon. Either that, or I got a bug, I dunno.