zangtian2
First: What is your IP, 192.168.2.61 or 192.168.2.64?
Second: http://192.168.2.61/flarum and http://192.168.2.61/flarum/ are not the same. If you have a relative path ./assets applied to the given location, it resolves to http://192.168.2.61/assets in the first case and to http://192.168.2.61/flarum/assets in the second.
As jordanjay29 said, you aren't allowed to be sloppy here.
Why is it doing that? Did you rewrite it that way?
Not if it's done properly.