To say that you know a friend of yours -so you still know him, for sure- since a long time, should you say "I've known him since a long time", "i've been knowing him since a lot of time" or "I know him since a long time"? and is there any difference if, instead of "a long of time" I say a specif date? There isn't really any background, just one of my usual doubts. I think the former is the most correct form, but still the fact that I know the guy at the present time, makes me a little confused. Maybe all of them are correct? Someone could please shed some light on this one for me? Thank you very much!