I'm writing to express my heartfelt gratitude to you.
The past three years we spent together has seen the enhancement of my English.
You immersed me in the charm of English,sparked my interest in reading and made me aware of the importance of critical thinking.
Had it not been for your help,I couldn't have made so much progress.
Thanks again for your help.I wish nothing but the best to you and look forward to seeing you again.