Since I knew you ..... this date has always been...

Since I have known you...this date has always been...

Can we use the highlighted part in this manner.. are they right? Pls suggest When to use 'since I knew you" and "since I have known you'.
Since I have known you seems the only correct version to me, probably because it suggests the intended meaning of knowing over a period of time more readily than the alternative.

In my opinion they may both be used, but the meaning of "since" differs. I take the first as a conjunction and the second as an adverb.

Because I knew you, I [have] always let you get away with it.

As long as I have know you, I've had a crush on you.