- How could you not tell me?
- How coudn’t you tell me?
Are the both meanings the same?
If not, what the difference?
Thanks! 
Both meanings are the same but the spelling in (2) is ‘couldn’t’.
Thank you.
So how come there are two ways to say the same thing?
Which one is more common to say?
Actully looking at that for a second time, I’m reconsidering… most times they mean the same thing (You must have noticed that there is often more than one way to say exactly the same thing in other discussions on this forum) - but now I’m looking again I’ve realised that with different emphasis the meaning might be slightly different.
How couldn’t you tell me? - the emphasis is on ‘tell’ - What stopped you from telling me?
This might also be the meaning of ‘how could you not tell…’
But there is another scenario:
How could you not tell me? - the emphasis could be on ‘not’ - You should have told me so why didn’t you?
That’s exactly what I thought.
I just wanted to make sure. Thanks!
Sorry I didn’t spot it straight away. Sometimes I guess things are so familiar that we take them for granted and just see what we expect.