可以有多种说法：（英文很可爱,不可以每个字都直接翻译,不然就会变成别的意思了）
You are not only a good teacher but my best/close friend.
You are a wonderful teacher, as well as my good friend.
Not only you're my teacher, you're my best friend.
I found a good friend in you, my dear teacher.
谢谢.