Do you want the long story or the short story? The short story; if you are having doubts now, it's probably not going to work. The long story:
I am in a very similar situation right now. This girl I am dating has GORGEOUS hair. Chestnut brown, dark, very silky. It's pretty thick, yet straight, and she curls the ends of it. So basically she has these curls that "bounce" when she walks. She knows she has good hair too. It's just a little past her bra strap, but she's short, so that's a pretty good length. She's never really had it any longer. However she did have it at a shoulder length bob at one point. I am 33, and I am in pretty good shape, as I run about 4 miles a day. It's not like she's overweight, she just has this belly on her. Its like all her body fat goes to exactly one place. As much as I love her hair, I am not sure how much we have in common, and how much longer we will probably be hanging out.
A few years ago, I dated a girl who had GORGEOUS, waist length, straight, brown hair. I was about 30, and she was 23 and right out of college. I had never been with a girl who had hair like that, and I would pretty much get hard every time I saw her. To this day, I say that you have not lived until you have been with a waist length girl. Unfortunately, our love for her hair was the only thing we shared in common, and it didnt last.
Shortly after that, I dated a girl who was a bit overweight, but had gorgeous, Italian hair past her bra strap. The hair was great, but I just wasnt attracted to her. Again, it didnt last long.
Very shortly after that, I met the girl of my dreams.....and she had a pixie. I wasnt a fan of her hair, but she had a gorgeous face. She was a "bigger" girl. Not fat by any means, just bigger boned (former soccer player). On our first date she told me that she had a 14 inch braid (not ponytail, braid) that she cut off and gave to locks of love recently. It was interesting that had come up, as I wasnt the one who started talking about her hair. Anyways, prior to that her hair (which was dark and THICK) was past her bra strap, approaching mid back length. On our first date, she told me that she was planning on growing her hair back to that length. We dated for a long time, and we broke up (definitely my fault). When we broke up, her hair was just about shoulder length. Shortly afterwards, she started dating another guy, and is now engaged to be married soon. The moral of the story is that while I have always been a "long hair guy" I wouldnt care what length she would currently sport for us to be together again. So no matter what you think your initial attraction is, and how strong you think your fetish is (I thought I HAD to be with a long haired girl to be happy), it's inside is what counts. HOwever, there has to be that initial attaction (which often for us, is long hair). If you are doubting it now, chances are its not going to last (which is exactly what I am going through right now as well).