I'm a dude and have grown my hair out since high school, but I keep it simple to a ponytail when I go out. A low one that's tied off at the nape of my neck.
I'll also note I've never had an opportunity to do a girl's hair. I'm the youngest boy among three older sisters, and I'm pretty sure they tended to do each other's hair and never had a reason for me to help. The only girlfriend I ever had for any length of time had trichotillomania, so she didn't have much natural hair on top of her head to style, and I wouldn't have wanted to risk damaging her wigs. Her natural hair did start to recover, I feel, while I was with her, since I think I was a calming presence for her, up until we fell out of love, but it was mostly just some very short curls barely covering her head.
It probably helped that I was also probably the only boyfriend she had up until then that could, and did, actively live with her for a couple years (or at least the first in a very long time that could spend that much time). Her last relationship before me was long-distance, so not exactly reassuring when you can't see your SO regularly, let alone daily like was our case.
... Anyway, long tangent aside, I can still totally get the appeal of being close enough to do your girlfriend or wife's hair, even if I have no personal experience. She trusts you with a part of her appearance, and that's quite something.
