using System.Text.RegularExpressions;

using System.Linq;

using System;

​

string input = "apikey:1234\\:5678;persoon:antoi\\;one\\";

​

//Parse

var headers = Regex.Split(input, "(?<=[^\\\\]);").Select(sets => {

    var parts = Regex.Split(sets.Replace("\\;", ";"), "(?<=[^\\\\]):")

        .Select(x => x.Replace("\\:", ":"))

        .ToArray();

    return new { key = parts[0], value = parts[1] };

})

.ToDictionary(k => k.key, v => v.value);

​

​

//Display

foreach (var header in headers)

{

    Console.WriteLine($"\"{header.Key}\" = \"{header.Value}\"");

}