Add field into other field with Views
One possibility is to use the Views Field View module:


  This module allows you to embed a view as a field in a view. A new field handler is made available, so this can also be used in area (header/footer/empty) handlers as well as rows.


Also, there is the 'Rewrite results' options in Views definition.

Alternatively by code, you can use use a field--[type|name[--content-type]|content-type].tpl.php file to override the rendering of the field. You would then have to access the $element['#object'] to get access to the other field that you would need to render manually. Reference: https://api.drupal.org/api/drupal/modules%21field%21theme%21field.tpl.php/7