It means that you promise to come but you didn't. That's right. 'Until now' is 'ещё' or 'пока' in Russian language. For example: Ты к нам еще не приехал = Ты к нам пока не приехал = You didn't come to us yet

Hello. Let's see. The problem is that we can't take the single word 'так ' itself, but the full frase 'так и не'! This is what we have to translate. It means that something was not done in a definite period of time or someone didn't do something in this period. In English we can use until now, so far, still, etc. ( as far as I know, of course ;) In Your example we have,' Ты к нам так и не приехал'. So it means that they expected him to visit them during the day for example but he didn't come neither in the morning, nor in the daytime, nor in the evening. Here some examples of using it: Ты так и не выучила русский ( I expected that You would learn Russian within 2 years, but You didn't). Книга так и не была прочитана ( I expected the book to be read in summer). Клинтон так и не стала президентом (no comments;) Трамп так и не отменил санкции. ( Russians expected Trump to take sanctions away in two weeks but he didn't do this) Thanks for the question.

так и не = not once / never

هنا معناها لسه مثلا Ты так ничего и не понял = ты всё ещё ничего не понял = ты до сих пор ничего не понял دانت لسه مفهمتش حاجة

Until now. It means you haven't come in till now as a result