Well yea but... She's a hardcore drug addict. And he's a dude she does hardcore drugs with. And we already know she loves boning under the influence lol. As I edited it before. She 98% did but if you wanna bank on that 2% be your own guest haha.
I mean she does heroin and pimps if you think she has a moral compas on sleeping around i hate to say it but you're delusional not saying shes a hoe. Like airith as she's hot unlike Airithe. So she could have standards but something tells me that Tommy meets those standards. The only thing i'd bank on is him not hitting her for fear of her throwing it in his girlfriends face.
Except, she's just clearly not attracted to Tommy. She may see him as a friend and a "partner in crime" but she never displays any kind of flirty behaviour around him. Even on the drug part, she didn't provide him any kind of favor. Refusing to give freebie or reduction. Despite her low inibihition, she still has a very pragmatic attitude with sex. During the first season, while she was already infatuated with the MC she still tried to get money from him. During the threesome with Riona she tried to maintain a "professional" facade until the MC implied she enjoyed it despite the fact he had to pay for it. On the roof, she asked money first until the MC made her admit she wanted it too. That was not casual sex because she sought a level a connection with the MC during sex nonetheless. She explicitly said she wanted to be the first girl he fucked while being high and the one he'll remember every time he blazes a fatty. That wasn't just "boning someone under influence".
So if you think she would casually bang Tommy just for fun, without trying to get something in return, you got her character wrong. She has no problem whoring herself if she can get something for it but Tommy has nothing to offer. As for Tommy, he keeps bragging every time he fucked someone ( Tania or Arieth for example ), if he had fucked Quinn in the past he would have mentioned it in front of the Diks. On the contrary, he was stunned in disbelief when he learned the MC fucked Quinn. A reaction he wouldn't have if Quinn casually had sex with anyone. Sure, he has a soft spot for her. He was deeply hurt when she "backstabbed" him about the prep party and swallowed his pride even apologized to her but she didn't play along. Refusing to apologize in return and even tried to charge him the double.
On the other hand, Quinn and Vinnie could have been a thing. With DPC sense of drama, I wouldn't be surprised if he was her former boyfriend before they started being rival dealers.