I told my partner about my desires shortly after dating her, but she's very open to new or weird concepts and she thought it would be a cool idea to grow her hair out. She's now rocking a thigh-length mane of pure black silk and I indulge in it every now and then. She supports my interest in her hair and takes care of it because she knows how much it means to me.

If you can manage to find someone like this who supports your interests, or you already have, it shouldn't be very difficult to bring it up to your significant other. Even if it means you have to help wash her hair lol.

But if she's not comfortable maintaining a length you desire, it's up to you to determine if that's a deal breaker or not.