1. Текст
2. Текст
3.1 Текст
4. Текст
5 Текст

/(.*)[.|] (.*)/s

/(.*).? (.*)/

/(.*)(.|) (.*)/s

/(.*?).? (.*)/

$string = "4.1   sdkjfglhgbkjlfgdf sfghjkghd";

list($number, $text)= explode(' ', $string, 2);

$number = strstr($string, ' ', true);
$text = strstr($string, ' ');

(^|n)(([0-9][.]?)+)+[s]+(.+)

//$str = 'Текст3';
//$str = 'Текст 3';
//$str = '3Текст';
//$str = '3/5 Текст';
$str = 'Текст 3.7';

preg_match_all('~(d+)?(?(1)(?:.d+)?|[^sd]+)~', $str, $arr);

echo '<pre>', print_r($arr[0], 1), '</pre>';
/*
Array
(
    [0] => Текст
    [1] => 3.7
)
*/