"I Don't Give A Shit Where The Stuff I Love Comes From. I Just Love The Stuff I Love." - Patton Oswalt

This couldn't be more applicable then right here. As far as I'm concerned Chewie is Han's Co-Pilot/ Best Friend/ Partner in Crime. That's it, it was more than evident on screen.

And this is also a good reason why I strongly dislike the EU (and to a certain extent you can add the PT to this too), because you don't need to explain or have explained to you every little detail from the OT. There's a reason it wasn't apart of the original movies because chances are it was either contrived or really boring.

edit: time for a new sig.