If Wes is in fact the straight guy...he has the most to gain from being "on", demonstratively affectionate, and emotionally expressive, because as we all the know, the straight guy has been aware of the "twist" from the very beginning...Wes is the only one of the remaining three that seems to genuinely play it up for the camera (and subsequently James)...which leads me to believe that his motivations aren't solely to connect with the "leading man", but rather to "perform" as much as possible with film crew in tow...perhaps that's just his personality...Wes adores the lens, Franklin seems indifferent to it (perhaps that's because he's got his eyes solely on the prize?), and Brian seems genuinely inhibited by the presence of a camera (as if it's a minor road block preventing him from establishing a deeper rapport with James)...so of course the straight guy is going to be the most telegenic and endearing, which, in turn, makes the show all the more riveting...
As far as the selection process for the final three goes...I originally assumed that Franklin was the straight guy by default because he was paired with Sean...but keep in mind...the producers do consult with James before he makes his selection (or at least have some kind of input)...Wes was paired with Robb...now Robb also has a big personality and James could have very well picked him...but as Andra mentioned, Robb seemed to be the least compatible with James and she's been a very influential element in James' decision making process...not to mention the fact that he never got to spend any real uninterrupted time alone with Robb as opposed to Wes, who got way more one-on-one time in very romantic situations (hello?...breakfast in bed anyone!)...it was obvious that James would choose Franklin over Sean seeing as how James was the most physically attracted to him from the get-go (James is no saint, he's shallow like the rest of us!!)...a classic no brainer!!!... if I'm not mistaken, Brian was paired with Darren...now this was the most surprising choice because it appeared that James and Darren had some raw chemistry...but he slipped by quite a few gaydars on this board (mine included) and it would make the final set-up that much more confusing...it's a lot easier for James and the audience to have two of the remaining guys seem like the more stereotypically obvious gay men so that they can establish Franklin as "the straight guy"...so I get the impression that the final three were chosen beforehand and grouped accordingly so that they would be chosen...
How's that for a conspiracy theory?!
(keep in mind...I'm probably all wrong...but that's my overwhelming assumption thus far!)
