Fusion Drive is corrupted
"I see everything working fine on the Mac but cannot update OS and neither do bootcamp."

If you can boot to the Fusion drive and read the contents of the disk, then the VERY FIRST THING you should do is make sure that you have a backup. Only then should you think about upgrading or messing with BootCamp.

"What can be done to fix this without losing all the data I have on the hard drive?"

Backup your disk. The only way to ensure that you will not lose any files is to have at least one copy on another physical device. Then, if something goes wrong with this disk, you will still have your files.

A Fusion drive is made of two separate devices: an SSD and a mechanical hard drive. Two devices means two separate points of failure. The mechanical hard drive is much more vulnerable to breakdown than the SSD. If one part of the Fusion drive breaks, then EVERYTHING is lost.

You may be able to 'repair' the Fusion by erasing the disk: or the errors may be so great that nothing will work. Either way, you can only try when you have a backup.

You may need to replace the mechanical drive -- ideally with a new, fast SSD -- or you can use an external SSD drive, which should still be faster.