User blog comment:Jam7/Jam's last-minute TDAS predictions/@comment-2002887-20130913191636/@comment-24600224-20130916154659

They were very clearly together. Courtney, several SEVERAL times in TDWT mentions that he's still with Duncan. On the first-class plane with Gwen (right after Duncan was reintroduced and after Gwen kissed him), Courtney tells Gwen something along the lines of "isn't it great that my boyfriend is back in the game?" to which Gwen doesn't declines.

If they weren't together, how could Courtney "break up on her own terms" if there's nothing to break up with?

Gwen also immediately felt remorse upon kissing Duncan. Why? Why feel remorse if, by your her own admission, Duncan was "free" at the time anyway?

And it's not just Courtney who acknowledged that they had a relationship. Duncan himself addresses this fact too. In Greece's Pieces, he persuades Gwen to "clear the air" which clearly meant that he fully intended to break up with Courtney for Gwen's satisfaction.

The evidence is just overwhelming that they were together that time that Gwen and Duncan hooked up. Duncan cheated with Courtney. That was kinda the point of the love triangle.