you are going to write an informal thank you letter to a friend. make some notes first, then write your letter thank you for... like / enjoy... next time...

hello my friend, I want to thank you for our friendship, I am glad that once I met you and continue to be friends, you are the best friend in my life, I hope our friendship will last a very long time and when we meet old age together, we will look at our children and great-grandchildren, I am grateful to you for your friendship with me.