It's fine to have specific preferences about your partner, even just cosmetic ones. It's fine to break up once they're no longer being met.

Some people seem to consider this taboo but physical and emotional attraction are both essential for a relationship to work. And any change in appearance can potentially drop the level of physical attraction to below your SO's minimal requirement. Obviously you seem to be walking a fine line there is a couple of inches of hair would be a deal-breaker.

What seems like a dodgy choice to me, but it seems to be a common one with teenagers your age, is to mold yourself into the person your partner would want you to be. Rather than being your own person, and letting the chips fall where they may.

Because no matter who YOU want to be and how YOU want to style yourself, someone amazing will fall for you because of it.