Student or Learner
you'll always be unique to me
you'll always be special to me
I'd like to write this for a girl. So I think the "special" is better for my situation.
"Special" can have negative connotations, in the UK at least. It can be understood to mean "having special needs" ie being below normal intelligence, having certain physical limitations and other such problems. It is used sarcastically.
Person 1 - My mate constantly falls over in the street for no apparent reason, and his spelling is terrible!
Person 2 - Oh, is he a bit "special"? (said in a very sarcastic tone of voice)
Another example, from personal experience: One of my friends has a pair of shoes which don't have laces or a buckle, they have a strap across the top which is secured to the main part of the shoe by Velcro (the sort of hook-and-eye system where two pieces of material fix together and can then be "ripped" apart). She refers to these as her "special" shoes, referring to the fact that some people with some physical/mental limitations are incapable of using buckles, or of tying shoelaces, so can often be seen wearing shoes with this very simple system.