It's surprising how much damage can be done by people who are trying to be nice. If you are dating someone who you like as a friend, and you know that person has much stronger feelings about you, don't think that the 'nice' thing to do is to continue to date them without explanation. That would be leading the person on -- intentionally or unintentionally. Always let the person know the extent of your feelings. You are not being nice when you pretend; you will both be better off when you are honest. Their time will not be wasted, and their feelings will be honored.