Multiple if in PHP template engine with Regex

Before all, sorry for my pretty bad english.

I'm trying to make a PHP template engine using regex & preg_match_all.

My regex looks like :

/\{:[\s]*?[\n]*?[\s]*?if(.*?):\}[\s]*?(.*?)[\s]*?(\{:[\s]?else[\s]?:\}[\s]*?(.*?)[\s]*?)\{:[\s]*?endif[\s]*?:\}/is

My PHP looks like :

preg_match_all('/\{:[\s]*?[\n]*?[\s]*?if(.*?):\}[\s]*?(.*?)[\s]*?(\{:[\s]?else[\s]?:\}[\s]*?(.*?)[\s]*?)\{:[\s]*?endif[\s]*?:\}/is', $template, $regs, PREG_PATTERN_ORDER);


for ($i = 0, $iMax = count($regs[0]); $i < $iMax; $i++) {
    $condition = $regs[1][$i];
    $trueval   = $regs[2][$i];
    $falseval  = $regs[4][$i] ?? false;
    $res = eval('return ('.$condition.');');

    if ($res===true) {
        $template = str_replace($regs[0][$i],$trueval,$template);

    } else {
        $template = str_replace($regs[0][$i],$falseval,$template);
    }
}

When in my template string I got only one if, something like this :

{: if $var > 3 :}
    The variable $var is > than 3
{: else :}
    The variable $var is < than 3
{: endif :}

It will work perfectly. But if in this if I put an other if, it will not work.

{: if $var > 3 :}
    The variable $var is > than 3
    {: if $var1 < 2 :}
        The variable $var1 < than 2
    {: else :}
        The variable $var1 > than 2
    {: endif :}
{: else :}
    The variable $var is < than 3
{: endif :}

In this case, the preg match all will not work properly, and will output me this :

{: if $var > 3 :}
    The variable $var is > than 3
    {: if $var1 < 2 :}
        The variable $var1 is < than 2
    {: else :}
        The variable $var1 is > than 2
    {: endif :}

It will stop at the first endif, not the good one. I have absolutely no idea on how to do this. If someone have an idea ? Thank you so much for your time and your help !