Is this inapropriate?? I'm close to my teacher... but not that close...?

It all started when I was 15 years old, I stood out in the clroom from a teacher not perversely but because I was the most dependable. All throughout high school I've been volunteering for the school and a lot of my time is spent with him. He phones the house to see if I am updated with others and if I know of upcoming events. If I am ever stuck in situations, he always comes around and gives a hand and he has even given me lifts when I'm stranded... I have never been in an uncomfortable situation however is this appropriate? I always thought it was okay but lately I've been worrying... has my dependability lead me into a taboo??? I'm graduating this year... could I carry on this same path in 2 years time when I no longer ociated with the school???