Well, I 'love' a few of my teachers, but 'love' like family, not your way. I will definitely keep in touch as I have with all of my teachers from the old school. You've got the e-mail, so that shouldn't be problem. And I think you might be mistaken about your feelings because you wasnt to be "like them" and that means you admire then greatly - people often admore their teachers. If you really fancied them you would want to be *with them*. But that's for you to sort out, I can only give you my opinion.
As for the card, only you can write one that's good enough. I gave a Christmas card to a teacher who is like a father to me that said: "Thank you for your kindness and support throughout the year. I hope your Christmas i a very special one, like you are to me." He really loved it. But practice it on a piece of paper first, think about what *you* want to say. By the way, I hope you are not at my school in Woodford Green and my teacher will not get a card from another student with the samt text! =P
Good luck!