Not sure what to do......

Hi All, I'm looking for advice, my financee and me have been having a hard time lately and now it seems she's not sure she wants to be with me. We have been together for 6 years and I have kids from a previous relationship. We haven't been good for a little while but I just thought that we were just going to a rough patch, this has happened before. Over the last couple of weeks we have falling out and then we talk and I think things might be getting better after a few days but then we fall out again. She has now told me that she wants to get married and have her own kids but doesn't think that can be with me and she wants to find someone else to do these things with. I know that she wants to be happy, be loved, get married, have children, I have told her that I want the same things but it seems that she doesn't believe me. This is killing me inside. She told me last night that she will always love and wants to be friends even if we aren't together, I'm not sure I could do this...... But then she also said there is something I can do to save our relationship but won't tell me what as I need to do it without being told by her. I have thought about arranging a date to get married but think this could push her away, but really don't know now. I feel like I just needed to write down what is going on at the moment.