I became friends with my ex gf, we had a couple stints afterwards of "hanging out" and we became best friends. I moved to Dallas, she followed me up here about half a year later and we got married. Be comfortable with yourself and what you want. Be confident in yourself and what you want. The rest will fall in place. If you think she could be the one, keep her in good standing, but I don't know about actively trying to be her friend. I had plenty of other things on my mind while my now wife and I were only friends. If you can't handle the heat, get out the kitchen though.
Going through something similar. Some good advice in here, at least some take it seriously. Some of you need to get a life, asking for pictures and being jerks to a guy who's clearly sincere. Realise that just because it's a forum with made up names, words have consequences and you are talking to real life people!
If she was not already in a relationship I would say go for it. The problem is she is. Best advice I can give is move on.
Yeah....there's not many worse ideas than trying to be "friends" with someone you are in love with.....especially when they are dating someone else. There's almost no scenario that ends well....and those few positive scenarios are by far the least likely. It sucks, but your best bet is to move on.