I think there are lots of issues here. One is just how important a part of your life and your heart are focused on folk music and how many other dimensions of your relationship DO work to your (mutual) satisfaction. It could be the tip of the iceberg, but who knows what the iceberg looks like? It could be indicative of greater dissastifaction within the relationship, or it could be just the "sign" to get the two of you talking and moving to an even greater appreciation and understanding of one another. Only you can say just how important your different tastes in music are to your relationship.
That being said, since I've been married and divorced twice and dated a number of men, I have come to a conclusion for myself. Music is such an important part of what gives my life joy, that I want to be able to share that with my (future) mate. This, for me, is of primary importance.
As others have said, there's absolutely nothing wrong with having different interests/passions. It's only a "problem" if you decide it is. Perhaps it's just an opportunity to examine what's important to you.
"Life is what happens while you're making other plans." -- attributed to John Lennon