The situation can go either way when you risk your friendship finding out that you are in love with him or with her: you can turn your friend into a lover and end up as a couple with a happy ending, or you can end up making things awkward for the both of you and ruin a perfectly good, platonic relationship.
So how will you know if your 'love' is worth risking your friendship? At the end of the day, it all depends on how strongly you feel for your friend. Use both your heart and your mind in making the decision. Can you bear the thought of losing a perfectly good friendship if you find out that your friend does not feel the same way? Once you blurt out your feelings, that will be the turning point of your relationship and your friendship - as it was before - can never be brought back. On the other hand, if your feelings are so strong that you just cannot bear the thought of your friend not knowing how you feel, then it is probably worth risking the friendship.
Whether your friend returns the romantic feelings that you have or not is a question which will be difficult to ask - but taking the risk of ruining your friendship is more acceptable than not letting your friend know how you feel. Who knows, if your friend secretly feels the same way about you, you just might be in for a happy ending.