Widget front-end fails to echo as expected from checkbox

on line 49 it seems you have hardcoded in the checkbox value it should actually look like this, it was always going to be true even if it did work as intended:

<input id="<?php echo $this->get_field_id('checkbox'); ?>" name="<?php echo $this->get_field_name('checkbox'); ?>" type="checkbox" value="<?php echo $checkbox; ?>" <?php checked( '1', $checkbox ); ?> />

also after line 81 add this in:

$checkbox = $instance['checkbox'];

Line numbers are based on what’s in pastebin