Well, as for who Bell Cranel ends up with in the manga, it's a matter of interpretation. Some fans think it's Ryuu Lion, while others believe it could be someone we haven't expected yet. But as of the latest chapters, no definite pairing has been firmly established.
It's a bit hard to define Bell's level precisely. It changes throughout the story as he gains experience and powers.
It could be a character from a rival group. They see Bell Cranel as a threat to their plans and so they betray him by setting him up in a dangerous situation.
I'm not sure who the author of the 'bell cranel light novel' is. There are many light novel authors out there and without more specific information, it's difficult to determine.
In the end of the Zatch Bell manga, there's a big showdown and the story ties up loose ends. The characters grow and achieve their goals in a way that feels right for the story.
Perhaps in the story, Bell Cranel had an arc or a relationship development that was so impactful that it left little room for the kind of creative interpretations that fanfiction often thrives on. Fanfiction usually takes the existing characters and settings and explores different scenarios, but if Bell Cranel's story in the official work is too complete or all - encompassing, it might discourage the creation of new fanfiction.
In the manga, Masamune's romantic journey leads him to end up with Sayuri. Their relationship develops through various challenges and sweet moments.
In the manga, Haruhi ends up with Tamaki. Their relationship develops throughout the story.
Sorry, I don't have the exact answer. You might need to keep following the manga to find out.
I'm not sure. It might depend on the author's creative decisions and the development of the story.
In the manga, Senku doesn't end up with anyone in a traditional romantic sense. His focus is mainly on science and saving the world.