Tell her that you were together during your earlier formative years, but these are still your (and her) formative years. And so it would be a good idea to not see each other right now and instead have other experiences. Make it also clear that you are absolutely not
ready for marriage talk. Tell her not to wait, that you do not expect that.
She might get weepy or angry. But you are allowed to break up with people without them emotionally holding you hostage. I suspect that some of what she wants is to be hanging around you and your family, but she can do that with her friends or with another guy.
Also - because I'm curious
nosy - who initiated the breakup last time? I am getting the feeling it was you. Getting back to her now was not exactly fair to her. So make up your mind - and also stay away. That means no drunk texting, no weepy, "I miss you!"
's or anything like that. I am not necessarily saying to stop all contact but you will need to tone it all down considerably before reconciling, if you do at all.