So it's not completely out of this world that "You're The Reason" can be a love song to a supportive significant other. Arguably it's a bigger stretch to make the song applicable to Tori and Trina's sisterly relationship, given their usual abrasive dynamic.
Nickelodeon did something at one point that made me feel a little weird - they re-recorded Tori's song for Trina with the tone of a love song and filmed the video with Victoria walking on a beach at sunset, a very romantic tone. I...they do remember what that song was about, right?
If I had just heard that song without context, I would completely think it was a song to a lover, so I thought the original context was stretching it more than anything else (especially given the performance...)
I also tend to look for a few redemptive qualities in Jade, because I feel like if she really his this horrible, evil person and that is the truth that her friends understand about her and they "put up with that", then they're all kind of horrible, too. It's easier for me to think they have a greater understanding of her and know that there's more to her than that, and more to Cat than her spaciness. Obviously, there must be more going on than the inability to count to three.
I entirely do this too - actually, I over do it. In-show, Jade will do things and I think that they're out of character, forgetting that the Jade of my headcanon is not ... exactly the character on the show.
And I agree about Cat as well - I think her homelife is really really messed up (the "I'm under my bed" muttering while Jade and Beck were fighting was a big hint) and her spaciness is a way of disassociating from it. I still find it annoying, but at least I can pretend there's a point beyond flanderization.