Girl advice - What should I do about this?

[Helen]

I know it's horrible when you really like someone, but despite how well you get on, you need to look at the facts here.
You left an open question about meeting up, to which she never responded. This was the first clue.
You met again entirely by chance (not a pre-arranged meeting), and asked whether she was seeing someone.
She indicates that even though it's complicated, there is someone.
Apparantly not satisfied with this answer, you then proceed to ask her friends whether she's single!
This is going to get back to her, and make you look very desperate indeed. It doesn't matter what her friends say - it's what SHE says that matters.
So once again you make a move by offering your number, and she declines due to this "complicated relationship".
It may not be official, and technically she may be single, but emotionally, this girl is completely unavailable.
I know it's not what you want to hear, but you need to back off.