Use external class in drupal 8 module with file name and class name
Your use statement is wrong. It should be:

use Drupal\mymodulename\lib\newman; - no Drupal on the end.

Aside from that, you should strive to inject dependencies in the constructor.

Also, there should not be a difference between the file name and classname. It makes it harder to debug and organize. The file should be named newman.php not drupal.php.

The error is referencing the fact that it cannot locate your class at the given namespace. It would help to brush up on PSR-4/autoloading in Drupal 8 as well as naming conventions and standards.