Where does it definitively show there was nothing between Quinn and Vinny? To my mind, we haven't seen anything like that and even if, as far as everyone else was concerned, they were just fuck-buddies, why would anyone still be talking about that? Both the MC and we the audience would only know that if people said something but nobody has because it's old news and it's not exactly something that someone just randomly brings up without the proper context.
Also, it might be nothing, but Quinn is in the background of this flashback with Heather who we know as Tommy's girlfriend, and since we have Tommy, Vinny, Heather, and Quinn in this scene, maybe that's hinting at this.