You want to let a close friend know how much she$/$he means to you in a way that is sincere and doesn't embarrass either of you. Following the advice on communication competence in your text, you would

react in the way that first occurred to you.

try to follow exactly the approach you used successfully with others in the past.

avoid sending any message until you were sure it would be well received.

follow the approach that you saw another friend use successfully, assuming it would work for you. consider a variety of alternatives, choosing the one that you think will be most successful under these circumstances.