Well, let"s clear the air with the obvious stuff. She"s immature as fuck and has some major attention needs. This guy provides friend-zone services willingly and happily. Given the information you"ve presented, I"m not comfortable definitively saying whether or not I believe that she would ever give it up for him.
With a "normal" bitch I would say she would never put out for a groveling, pitiful loser like him, but for someone that refuses to let go of a dude like that... well, let"s just say her subconscious knows that he"s been paying it forward for quite a while now, and with her super-human need for attention it"s hard to say what she"s capable of. The fact that she readily admits that he has split up her past relationships is all the proof you should need that she places that relationship as a higher priority over her romantic relationships.
At the end of the day, you"re not going to get this dude out of her life because she"s not interested in getting this dude out of her life. You"re going to have to accept that fact and go from there. Personally, I wouldn"t be cool with a bitch who had a stage five clinger like him. I would tax that ass and move on. If you"re really convinced that this is THE ONE and a keeper, you"re going to have to get creative with your cockblocking of his communication with her (I"m sure FoH can help with this).
Not pertinent to the short term:
Spoiler Alert, click show to read:
Edit: The Not-So-Obvious-Stuff: I"m gonna go out on a limb and say that you haven"t dated/been with too many women. That"s fine; we all start somewhere. Take it from someone who felt like romantic relationships was the end-all-be-all to life... do not convince yourself that this is the perfect bitch until you"ve been with her for at least a year. If you"re as inexperienced as you present yourself, I"m sure that sounds very daunting, but trust me, you do not want to commit to someone that willeventuallymature and the dynamic of your relationshipWILLchange. To you this change will seem unexpected and over-night, but I promise you it will be a slow gradual thing and your friends will be trying to signal you that something is amiss. Your heart will be broken, and you"ll come here to tell us about it.
Ideally, rent a place and live with this chick (not now, obviously, but when it"s appropriate for the relationship) before you commit to anything serious. I haven"t run into too many old fashioned dudes these days who want to get married, then move in with their lady, but I would strongly advise against this. Count me as someone who would not be married today if I had the sense to live with my fiancee before I married her.