How long are you together

How long have you been together for ? from a pt. in the past till date - time elapsed.

How long are you together for ? from this pt. in time - till when you'd be together.

reexplain, i havent understood.

How long have you been together for ?

Assuming that the people being talked about in the sentence met at some pt. in time in the past, and still know each other. In simple words, people met in the past, and are still together.

For example - If I met someone in 2008, and I'm still with her, I'd say "We have been together for two years now"

How long are you together for

Present perfect...I amazengly undersand.
but the problem is now present progressive or present simple which is "how long are you together"
I can say :"we are together for 30 years" or "we have been together for 30 years"
but "we are together for 30 years" sounds wierd because it refers to the present (whether it is simple or progressive) so 30 years is the past - present if still tog

PicnicHow long have you been together?
How long are you together?
...
What is the difference...

The difference is that the second one is wrong. "to be together" means "to be together as a couple", for example, married or engaged to be married or living together.

But i don't understand why its incorrect