Sounds like she has another guy on the hook, or like you think still likes the f ucked her over dude. If she doesn't want to make it official then how can you be exclusive? She doesn't think of you as her bf. Wonder if you started going out with others would she suddenly want to make it official and want to be called your gf, do you have others interested in you also? Ask if she's over that guy, tell her to be honest and go from there.
Life is a song - sing it. Life is a game - play it. Life is a challenge - meet it. Life is a dream - realize it. Life is a sacrifice - offer it. Life is love - enjoy it.