What should you do if a girl says she wanted to marry but she wanted to end the ex-relationship?

It appears so many of youth today do everything backasswards. They live together, have their kids, buy their house then get married. So, I suggest to you that she break off her relationship with her ex (technically he is not her ex because she is still going with him) and then I'd take it slow and easy about getting married. You would be getting a person on the rebound. You need to get to know each other better before you take the marriage vows.