$re = '/(\d{2}-\d{2}-\d{4})\s?(\d{2}:\d{2})\s?:([^:]+):((?:(?!\d{2}-\d{2}-\d{4})[\s\S])+)/';
$str = '14-08-2015 14:18 : Example : Hello =) How are you?
What are you 2 doing?
14-08-2015 14:19: Example2 : I\'m fine thanks!';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php