I think everyone has preferences, but I don't think a persons preference should take anything away from who that person actually is (does that make sense, lol). If it's to the point where it's bothering one person in the relationship enough that they feel the need to verbally (or physically) jab the other person, well, IMO, it's kind of shallow and I probably wouldn't waste my time any longer in the relationship. There are plenty of other women out there who would like you, long hair and all.
Personally, I prefer a shaved head, not Mr Clean style, but #1 or #2 on the clippers. But, my hubby did go through a period where his hair was all one length and to his shoulders, I could have cared less, I didn't and don't love him for his hair, I love him for the person he is.