Present Perfect again

[henryh]

Is it okay if I ask a negative question with How long + Present perfect?

I know it's right saying: Haven't we met before? But with the question word 'How long?'

E.g. How long haven't you meet you brother?

Is it common?

Or does it sound better by saying:

How long has it been since you last saw your brother?

Are both ways correct or there's a difference in meaning?

Thank you.

[Clare James]

The sentence 'How long haven't you met your brother?' isn't correct. We use How long...? only for positive forms.
The second sentence 'How long has it been since you last saw your brother?' is fine.