"You are my incomparable pen and ink and the most beautiful legend in my poems" means that the other person is the best creative material in my heart and the most beautiful symbol in my poems. This sentence expresses deep praise and cherish for each other, and also expresses the importance and particularity of each other in their own hearts.
This sentence also expresses the importance and particularity of each other in their own hearts. It means that the other person is the best creation in his own pen and the most beautiful symbol in his own poetry. It can be understood that the other person is the most perfect and irreplaceable existence in his heart.