It would be unreasonable to think that Chad and Sage never had sex. I don't think she would have put up with it based on her fairly abundant sex drive. Just because Chad is gay doesn't mean he can't be intimate with a woman. Chad was probably able to perform to some degree, though Sage said multiple times how he wasn't satisfying her lately as he had mentally moved on from her to his new relationship.
There was probably a lot of pressure for the president of the jocks and the president of the HOTs to be a couple; maybe that was one of the unwritten traditions between the two groups. To be fair to Sage, Chad is a tall, muscular guy and he seems fairly intelligent unlike some of the other jocks, so he would be easy for her to have a relationship with considering all of the other external factors driving them together.
I couldn't care one way or the other if Sage was tossing Chad's salad while he was lifting weights, but I really do think there are too many signs indicating that their relationship has been sexless to suggest it's an unreasonable suggestion.
Here's the entire exchange between Sage and Chad when he comes asking for her help:
Chad: "Please, Sage! Can't you at least talk to them?"
Chad: "Do you want me to lose everything?"
Sage: "That's why you're here?"
Chad: "Yes!"
Sage: "What about me?"
Chad: "What about you?"
Sage: "You're never here just for me..."
Sage: "I don't fucking get you!"
Sage: "It's like I'm only good enough for you at parties and when we're with your friends."
Chad: "Sage, this isn't about us. It's about my future!"
Sage: "You put yourself into this situation."
Sage: "I can't fix that for you."
Chad: "Yes, you can! They will listen to you."
Sage: "..."
Sage: "I'm not promising anything."
Chad: "But you'll try, right?"
Sage: "For you...of course."
Chad: "Thank you."
Chad: "*Smack*" (Chad kissed her on the forehead)
Sage: "Hey! What the fuck!?"
Chad: "What?"
Sage: "I try to help you and that's all I get?"
Chad: "What do you want?"
Sage: "A real fucking kiss! Not just a peck on my forehead!"
Sage: "Oh! And it's about fucking time you start getting more physical with me, too!"
Chad: "That's how you want to do this?"
Chad: "Attaching strings to your helping hand?"
Sage: "Who the fuck talks like that!?"
Sage: "And no, that's not how I want to do this..."
Sage: "...but look at yourself! Do you call yourself a man?"
Sage: "You've got this sexy woman in front of you trying to throw herself into your arms..."
Sage: "...and you can't wait to leave instead of trying to get inside of her panties!"
Chad: "I already told you why that is."
Sage: "Stop with the fucking steroid bullshit! I know that's not the truth."
Chad: "I'm not lying! How would you know!?"
Sage: "I know because..."
Sage: "I-I..."
Sage: "I talked to Arieth!"
Sage: "She says Dawe fucks her all the time!"
Sage: "Sure, he has some issues with his tiny penis, but they still fuck!"
Chad: "Dawe isn't taking the same things I am. He's on the pill, you know?"
Chad: "It's not as potent."
Sage: "On the pill? Like a fucking girl?"
Chad: "Hey! Don't mock Dawe. He's a nice guy."
Chad: "And yes, he takes the pill. It's a cheaper alternative and an effective way to build some extra muscles."
Chad: "Maybe it doesn't make his dick as soft, but..."
Chad: "This isn't about Dawe and his flaccid cock!"
Sage: "You're right! It's about you and yours."
Chad: "Gimme a break! You think this puts me in the mood?"
Chad: "I'm on the verge of losing everything I worked so hard to build up."
Sage: "Worked so hard, huh? Steroids is cheating, you moron."
Sage: "You think that will go unnoticed forever?"
Sage: "You think they don't test for that at your precious fucking competition!?"
Sage: "You made those choices and brought all of this upon yourself."
Chad: "I can't fucking deal with you right now."
Chad: "I have to sign up for a dorm. I need somewhere to live."
Sage: "It's funny that you didn't ask for help with getting a place to stay!"
Sage: "Maybe I would have let you sleep with me!"
Chad: "Take some time to cool down, Sage. Thanks for nothing."
Sage: "Fuck off!!!"
There's a lot in there indicating fuck all has been going on between the two:
Sage: "What about me?"
Chad: "What about you?"
Sage is the last thing on his mind, because that's how it always is.
Sage: "I don't fucking get you!"
Sage: "It's like I'm only good enough for you at parties and when we're with your friends."
So she's definitely just there for the public and he's not interested in her in private.
Chad: "*Smack*" (Chad kissed her on the forehead)
Sage: "Hey! What the fuck!?"
Chad: "What?"
Sage: "I try to help you and that's all I get?"
Chad: "What do you want?"
Such a platonic thankyou to the sexbomb standing in front of him, and he can't imagine she'd want anything else, because he doesn't want anything else.
Sage: "Oh! And it's about fucking time you start getting more physical with me, too!"
Chad: "That's how you want to do this?"
Chad: "Attaching strings to your helping hand?"
Sage is basically begging for sex and he's like, "Oh, fucking strings attached!" - He really doesn't want to fuck her, like ever, with an attitude like that.
Sage: "You've got this sexy woman in front of you trying to throw herself into your arms..."
Sage: "...and you can't wait to leave instead of trying to get inside of her panties!"
Chad: "I already told you why that is."
Sage: "Stop with the fucking steroid bullshit! I know that's not the truth."
Then he uses his old ruse, the steroids won't let me fuck you. How long has he been using that excuse?
Chad: "I have to sign up for a dorm. I need somewhere to live."
Sage: "It's funny that you didn't ask for help with getting a place to stay!"
Sage: "Maybe I would have let you sleep with me!"
Chad: "Take some time to cool down, Sage. Thanks for nothing."
Sage: "Fuck off!!!"
Yeah, it is funny he didn't ask his girlfriend if he could stay with her. Fuckface went straight to her when he needed a place to stay, but her so-called boyfriend couldn't wait to do a runner.
I'd say Sage has put up with their bullshit relationship because it looks good being with the Alpha's president, and she's still living the life. They've obviously talked about sex before and he's knocked her back before using the steroids as an excuse. But now that she's starting to suspect he's cheating on her, she's starting to get less tolerant.
I don't think it's unreasonable to suggest all of that, depending on how long it's been going on for, and we just don't know.
My guess is that Quinn was supposed to be a main antagonist but she proved too popular so DPC changed it.
I'm not inclined to go along with that train of thought. I think DPC knew exactly what he was creating with Quinn from the get go. Her progression has been too nuanced for a character arc that just changed due to client feedback. She's Maya's antagonist, not the mc's.
On the mc and Quinn's first meeting she's giving him a handjob, and on their second meeting she's fucking him in public. And when he teases her that shee needs to go deeper, she responds:
Quinn: "I knew from the start that you were my kind of guy."
And this is only episode 2.