I still don't know the exact answer to that, but as far as I've seen from the old episodes, Bo and Carly's love is not only deep and mature, but also predestined, if you take a good look at their three memorable encounters( I explored this in my Bo and Carly fan fiction).
Even when they were together back in the day, it was more than obvious that Bo and Carly had a very special bond, the way they looked at each other, all the things they said to each other the whole time, especially during the beautiful symbolic wedding they had on top of El Castillo (which I hope they'll go back to some day).
The love, bond and the chemistry has always been there but the DAYS writers don't seem to care about their history but thank God that we still do. When we say we want Bo and Carly to stay together for a a very long time, it's because we have valid reasons, not because of any form of bias against Hope. So please, I need everyone to do this: in the comment line, write exactly what you think makes Bo and Carly so special. And please view this 'lost' montage. I had to upload it in You Tube using another track, thanks to their annoyingly strict rules. Remember, feel free to make your voices heard!