Is it normal to like the mysterious scent of my gf's hair?

That's just her body odor, and the pheromones from the sweat on her scalp mixed with her natural oil from her scalp.

It could be tricophilia (abnormal love for hair).

My husband says, one of the ways he can tell if hes really into a woman is if he likes( or is turned off) by the smell if her hair/ scalp. Guess he liked me.
I think its normal and its her skin scent, hair ouks and maybe some sweat but in a nice way.

The human sense of smell is very strange.

We have something like 450 different types of olfactory receptors in our sinuses, but humans are primarily visual creatures, so we don't pay a lot of conscious attention to what we smell.

There's a large variation in people's awareness of smells in general and their sensitivity to particular aromas. For example, my general sense of smell isn't all that good, but I'm very "tuned-in" to the aroma of rancidity (fats and oils that have oxidised). My wife isn't, so on a couple of occasions she's happily used ingredients in the kitchen that smelled really bad to me. On the other hand, there are smells that I hardly notice but she finds overpoweringly obnoxious.

Things get even stranger when it comes to the aromas of other people - particularly potential mates. For a long time, the scientific consensus was that human pheromones don't exist. That's logical, since we certainly don't respond to aromas in the dramatic and obvious ways that insects and many other mammals do, but it's a very difficult field to research and there are some hints that scents may have subtle effects on us that we're not consciously aware of.

I won't go into the details here, but Google "t-shirt experiment" if you'd like to read about one of the most intriguing experiments that was carried out a few decades ago. The search results that came up for me just now also had links to many related articles on the subject of scents and dating.

What is clear is that we do all have a particular scent (as proven by the ability of dogs to track a particular person), even though most of us mask that aroma by applying other smelly substances to our bodies and clothing. The most important thing in this case is that you like the smell of your girlfriend. Ideally, she also likes the smell of your body - even if she's not an olfactory-oriented person and she's not consciously aware of doing so.

Pheromones maybe. Yes our hair smells nice after a shower.