I don't think you are in any way obligated to make your feelings known, since we are not obliged to tell someone we know everything we think about them. For example, there might be things about a person who is a friend yet which we do not like, and we are not obliged to make this known to them, and many friendships and indeed more romantic relationships would collapse were perfect frankness to be pursued.

There is something rather exciting about unrequited love and also noble about remaining silent in a situation where the object of love is unaware of one's feelings. It might not be much of a consolation, but it is worth reflecting on how banal a relationship can be when both parties are in love with each other, while by contrast where one is and the other is not all sorts of interesting possibities arise.