Valentines and the student

i'm all filled with squishy feelings of love and happiness (or mcdonalds breakfast) about my family today, but this squeezed a question into my brain (yes it got past the egg mcmuffin and orange juice) to see how we treat students on this day of love. i know that my daughter wrote a valentines card for her kindergarden teacher, and this will probally continue at least through elementary school but when comes the point of not being OK to say they love their teacher? i guess being the highschool teacher its more of a concern to us who deal with older kids but i think that we try to be kind and caring to all students on ALL days not just feb 14 but where do we draw the line when they want to tell us more than we need to know to be just their teacher. Some kids don't have a solid parent figure that they can go and talk to about problems in life (gotta love the teenage years), so it is a bit of a compliment that they feel comfortable enough with you to broach the subject but then comes the issue that they may begin to see you less as a teacher and more friend and lose respect for your teaching authority, and in few cases the feelings grow from friends to more which is a major issue so where is a good place to draw the line so they feel supported and cared for in the class but not too much so that new emotions grow....maybe Data from star trek has it best, no emotion so it can only be logic.