I think its pretty clear from what you wrote that you know what the problem is.

I can relate to her attitude because I have a similar character. And from how you described her and yourself, it sounds familiar.

I think she the fact that she has ADD, has told you that she wants space from her other friend, has a hard time being honest, that she recognzes shes a "bad friend" are all tell tale signs that ... I wouldnt say shes not interested in you, but then again its hard to find other words.

I think its best that you look out for yourself, as hard as it may be to swallow, I think she really needs her space and you should leave it.

I would let her know that you are still open (and available) but that you need to take care of yourself and that you wont contact her anymore. Let her be the one to take the initiative and give her space (having a similar character, I can relate to the feeling of needing space).

She may feel smothered or not like the excessive attention and really just want space.

So my advice would be to let her go and get her out of your mind. Like the saying goes, "if you love something, let it go, if its meant to be, it will."

Focus on bettering yourself and not "forcing a horse to drink" and you might be suprised that she contacts you.