To be honest with you

When you are certain to be incapable of reciprocating the feelings of another, is it best to keep it to yourself and hope that his feelings for you eventually go away? Is it okay to allow someone to fall in love with you knowing you coudn't love him back?

Leading someone on is the worst act one can do if blessed with the awkward situation of having someone fall in love with you. It is not cruelty to tell someone that you do not love them and would never be able to. It is better to let people know where they stand. It avoids making them feel like they've been had. It keeps you from looking like a jerk when they do decide to stand by you despite all knowledge that they are to enter a one-way street.