My take on the recent Quinn discussion.
Sure she's not an official, report-at-the-end-of-each-episode, bona fide Love Interest (with a capital L & I), but for supposedly not dating, Quinn and the mc are together a lot and she's breaking her own rules for him (now this is assuming you're making an effort with her, those who avoid her like the plague aren't gonna have significant scenes with her):
Episode 2, she fucks him in front of an audience. But the audience doesn't know. It's a personal scene between the two of them. Granted it's also a show of power, but do you think if she was with Derek in that scene she would have fucked him too?
Episode 3, Quinn has a threesome with the mc and Riona. It's not something she normally does. In the past she may have pimped herself out, but it seems these days she's off the menu, and it was only due to desperation (for money, not necessarily for dick), and a growing infatuation with the mc, that she did it, but that scene gets a little more intimate than Quinn is used to.
Episode 4, Quinn and the mc banter in front of the HOTs, and Quinn even refers to the two of them as sweethearts (albeit in a joking matter, but you can change the tone of this scene if you choose a very loving pet name for her to use, I usually just stick with "pervert" though).
Later on in the episode they get high on the roof and she's genuinely concerned for him when the high hits. Unlike Tommy and Riona who don't give a fuck and go off to laugh at Derek, Quinn stays with the mc to make sure he's ok. Of course that evolves into them fucking on the roof. She tells him she doesn't give blowjobs to anyone (meaning she doesn't do it often, at least not anymore), but she accommodates everything the mc asks for in that scene.
Later on the in the free roam, she attacks him when he wanders into her room, but it turns sexual. She keeps up her controlling act, but when he leaves, you can see she would have liked things to be different, she's just too afraid to behave differently.
Episode 6, Quinn accepts the mc's help when she's mugged. She's starting to feel more comfortable around him, at least one-on-one, and obviously it turns to sex. She doesn't want to stay with him, still worried about appearances, but it looks like she might even have second thoughts right before she leaves.
Episode 7, they hang out together in her room, smoke, make out (involving kissing which she's not accustomed to), and eventually have sex. She initially tries to stop him from sleeping there, once again worrying about her reputation, but when she realises he's totally out of it, she cuddles up to him and naps as well.
During that scene, when she asks who the mc would like a free fuck with, if you answer "her" (of course you answered "her"), her response is, "That's...not what I meant. Um... You don't have to pay me for that." Their relationship is no longer associated with a financial transaction. Of course he can still be a customer, but not when it comes to her personally.
In the HOTs party, she hangs out with him in the kitchen, she even holds on to him despite her protests. When the photo makes its way to Rooster, by the looks of everyone's responses, this is far from her usual behaviour.
Later if the mc fucks Sage outdoors, when Quinn and Riona walk in on them, Quinn is a little caught off guard and feels a bit uncomfortable.
Episode 8, Quinn and the mc meet up in the library and then decide to head off to hang out together. They relax together and chat on a park bench, Quinn opens up about her feelings on things and they end up making out in public (a brief kiss really), pushing her limits for the mc.
Further along Sage, Quinn and the mc start planning the Halloween party, and of course it evolves into a threesome. Mostly it's Quinn showing off to Sage, but after that, Quinn and the mc spend some quiet time in the HOTs garden where the mc holds Quinn and she rests her head on him.
We know that Quinn could balk at any moment, she totally bales on him if she finds out he's dating Jill. I think that scares the shit out of her, how could she compete with the rich, buxom princess of B&R, so she'd rather end it on her own terms than suffer a rejection down the line.
But all all-in-all, there's definitely a decent relationship there between the mc and Quinn. It is by far the most advanced relationship between any of the girls outside the main LI circle, and arguably just as advanced as the main LIs.
She's an unofficial LI by all accounts.