Any man that says they haven't been in this situation is a liar. It happens to us all at some point, but really just learn from the experience and improve. That's all that you can do.
The WORST thing you can do is think you can turn this around. She knows you like her, and wanted more... and she is sending you clear signals she isn't available, so you're done. All you can do is try to forget about her... my recommendation would be to stop looking at her social media feed and when you find yourself thinking about her and wishing you had done something different, just get busy with something else that is productive. If she reaches out, try to make a date... if she won't commit to this, just move on. Trust me... if you've been sniffing around doing sh1t for this chick any length of time, she'll try and pull you back in.
Now if she really values you as a friend, she might get upset that you are walking away, just like she would be upset by one of her valued GFs that moved on... if this is the case, she'll reach out and ask "What's wrong, are you mad?" or some such BS... if she does this this is what you say:
"I'm not going to insult your intelligence by telling you what you already know. Do you really want some dude hanging around hoping things change, pretending to be your friend. It's not fair to you and it isn't fair to me. If things change and you are really available, reach out, and if I'm not involved with someone else then we can go from there."
Then you are done... walk away and never look back. But the truth is in most cases, she'll just let you drift off.
Don't hate her for this, she can't help it... it's just the way chicks are... you can't control her, only how you respond to it.