I am considering breaking up...

I have been trying to convince my girlfriend about why we should take our relationship to the next stage and get engaged, but she says she has never thought about it and won’t think about it for a few years. She says she doesn’t believe in the concept, which is strange because I assumed we were together for a reason. She says she loves me but also doesn’t believe in institutions like marriage because they feel like a power struggle. I accept her argument but believe in a lifelong commitment. I don’t think her arrangement works for me and even though I love her very much and would have liked to live with her, I am considering breaking up to avoid any resentment in the future. Is this a wise decision?
She is being clear about her expectations and what she wants out of this. If they don’t work for you, it is the right decision because, as you point out, it may lead to unnecessary resentment in the future. This isn’t a decision to take lightly though, because our wants and expectations can evolve and change as we get older, or as we spend more time with another person. You are under no pressure to decide immediately, and it may be more sensible to spend more time with your girlfriend and try looking at this from her perspective. What is it about her decision that makes sense to her? When you get a better understanding of that, it may help you think of your own future differently.

I ended a relationship four months ago. How long should I wait before deciding to date again?
That depends entirely on your state of mind, how ready you are to move on, and whether you know what you want from this next relationship. Is it just companionship, someone to help you forget about your ex, or a genuine connection? There is no manual that defines a specific period.