In these lines, the speaker describes Damyan as a man filed with woe, languishing for love. He is enraptured with May, the wife of his master, January, but of course, he struggles to tell her of his infatuation. She will only deny him, he thinks.
Damyan becomes physically sick because of his love for May. His body burns, and his life is at risk. He has allowed love (or more likely, lust) to overcome him and weaken him. Finally, he can no longer endure the pain of his love. He must express himself, and he writes everything out in a letter to May in the form of a song. He then puts the letter in a silk purse near his heart and waits for the opportunity to give it to May.
This little passage tells us quite a few things about Damyan. First, he is a sentimental fellow, who allows his emotions and his passions to get the best of him. He does not act on reason. He does not look at his situation with an objective eye. Rather, he lets himself get caught up in his desire for a married woman, and he lacks self-control so far as to actually make himself sick over his unrequited love.
Further, Damyan is both an expressive man and a fearful man. He wants to tell May all about his love for her, but he is terrified of rejection. Finally, he writes a letter (in poetry no less) and places it near his heart (so sentimental!). Now he must wait for just the right time to give it to her, for his letter says what he is too scared to say out loud.