Нужен знаток английского :) Вопрос про грамматику.

Есть текст: "I have a lot of friends, but the best friend of mine is Irina. She has blue eyes, a round face, fair hair and a broad smile. She is short and slim. I have known her for a long time, since our first school years. But we became true friends four years ago. We have much in common: we like English and psychology, sport and dancing. We are looking at this world in the same way and first estimate a person's mind, their kindness. We don't understand meanness and treachery. For many years we have been sitting at the same desk: Irina and me. But it's only recollections now. On a May morning the last bell rang for us for the last time and in the farewell waltz the last school ball was dancing".

Нужно определить время глагола have been sitting и аргументировать свой ответ.