Why is she always changing her mind?

I have been in a long-term relationship with a woman who keeps changing her mind. When we began dating, she wanted to end it after two years because she felt we should be seeing other people. We got back soon after that and have been together for five years now, but she says this relationship won’t evolve into anything official because she doesn’t believe in the institution of marriage. I don’t care about that stuff because I am more interested in simply being with her, but I sometimes wonder if I am being unfair to myself by accepting everything she says. I want to spend my life with her but have no way of knowing if she will change her mind when we turn 50. Am I being foolish?
You’re with her because you want to be. She presumably feels the same way. This isn’t a conversation about marriage and the legality it offers because nothing is permanent if one partner in a relationship doesn’t want it to be. What makes you believe a more stable relationship with someone else will also be one that lasts the rest of your life? Speculation can cause all kinds of concerns, but I suppose the thing to ask yourself is why you choose to be with this person and what value you bring to each other’s lives. I also suggest you speak to her about your concerns, because a long-term relationship is of little value if you can’t both be honest about how you feel.

My girlfriend’s brother recently did something horrible and I have been trying to find a way of telling her this without making her hate me. She worships him and I am afraid that picture will collapse after she hears what I have to say. She may blame me for how she feels about him later. What should I do?
If she’s sensible enough to recognize that his behaviour doesn’t have anything to do with you, why assume there will be a problem if you speak out?