It's good that she's a fiance, not a wife.
I was in a similar position years ago, I didn't commit to the GF until I had made up MY mind as to what I wanted to do. So aviation was part of the deal out of the chute with her.
You probably first need to decide what's more important, her or aviation. If the answer is her, than aviation is her call. If it's aviation, then just tell her how it is and let the chips fall where they may.