Dear Mr. Black，I’m very thank to you for inviting me to stay

Dear Mr. Black，
I’m very thank to you for inviting me to stay with you in the come summer vacation. I have been dreamed of seeing you again so that I can get help from you in my English learning. And I’m afraid I cannot go to your place in this summer. I’ve promised my grandmother, she lives in the country, to spend this summer with her. She misses me too much that I find difficult to refuse her request. I’m busy preparing for my examinations in present. I planned to visit you in winter if it’s convenient to you.
Best wishes.
Yours truly,
Li Ying