The struggle I have internally is more about me. Am I the type of person who will fight for my R or am I the type of person who will walk away?
I don't see this as being about the type of person you are.
I think the bigger question is if this particular R is the one to fight for?
It may be that neither one of you wanted to get married because this wasn't meant to be a "together the rest of our lives" kind of relationship. Just something to consider...
There is no arriving, ever. It is all a continual becoming.