Here is your answer with some delay. I was just within "one month don’t answer any question of the year of my life !! "
Go to character BP and follow my steps:
1 - Follow this graph which controls the mouse input values. I noticed a strange behavior when unchecked all inherit control rotation check boxes from camera boom. I noticed ‘get world rotation’ gives nonsense values while ‘get relative rotation’ gives me world rotation values !! That’s why you may get confused a little when see my graph. That is a bug i guess.
2 - select your camera boom and set the settings below:
3 - erase everything within movement input section of the character BP graph and replace it with mine:
4 - select ‘class default’ tab from the toolbar above and follow this picture:
Now you are all set. But a problem will rise when trying to limit camera boom rotation values. Which is, when your character tries to move backward (toward camera) he will enter an infinite loop. And that’s totally understandable. I leave this problem for you to solve. But to give you a direction where to look for it, you may need to make some changes in the third picture.
Regards,