As someone who has observed young women who have had guys they liked as a brother or a friend fall in love with them and shower them with excessive unwanted attention, I can tell you that Gwen and Cody would never work. Gwen clearly considers Cody to be nice and one of the few sane people she met while on TDI. However she has no romantic interest in him because she just plain isn't attracted to him. In fact, she even described him as reminding her of an ANNOYING LITTLE BROTHER. If a woman sees a man in that light, there's not going to be any romantic or sexual interest. None. Zero. Zip.
Cody is a preppie, he's over-eager, he tries to hard to impress Gwen and falls flat on his face almost every single time. Trent is a musician, he is (in TDI) more reserved than Cody, he's taller than Gwen while Cody is shorter (sorry folks, but most women prefer a guy who's taller than she is), he's more muscular (many women prefer a bigger guy) and he has more common interests with her.
Trent clearly likes Gwen and while he showed interest in her, he did so slowly, didn't do anything (in TDI) to make her uncomfortable, was friendly but not over-eager (in TDI) and gave her space to just be with him as opposed to pressuring her like Cody did. When they finally hooked up, it was her who kissed him first, and in my experience that kind of thing shows that Trent was who her true interest was in.
If any of you have been in a situation where a friend or coworker was constantly showering you with unwanted romantic feelings, pressuring you to get with them or hook up with them when you didn't feel any interest in them (I have been through this on the receiving end), you know how annoying, stressful and uncomfortable it makes you feel. When somebody like that keeps on coming on strong to you, it makes you dread being around them and doesn't do anything to enhance your romantic interest in them. If anything, it maks you start to hate them. In a work or school environment, what Cody was doing could be considered harassment and even on a reality show, if someone goes over the top in romantic interests with someone or in personal interactions, they can be removed from the show (it's happened on The Real World and Road Rules before.)
The bottom line is that while Cody does have some things going for him--he is nice and he truly selflessly cares for Gwen, she just doesn't like him that way and given how over-eager he was on TDI, he may never get that kind of a chance with her because of it. Cody would have had a better shot if he'd been interested in Beth or Katie, but instead he went after someone who was clearly not interested in him and now he looks like a fool in her eyes.
Despite Trent's meltdown, what I saw with Gwen before she got kicked off was some remorse and regret for how things went down. Some of it was Trent's own fault, but I think Gwen also saw some of her own fault in this as well. I'm very interested in seeing what happens in the next TDI Aftermath. I have a feeling that if she and Trent get some alone time and they hash through things honestly without others getting into their faces or business, they will probably get back together because they are well suited for eachother. Just my $0.02...