YOU SAID:
Nick is my best friend
INTO JAPANESE
ニックは私の親友
BACK INTO ENGLISH
Nick is my best friend.
INTO JAPANESE
ニックは私の親友です。
BACK INTO ENGLISH
Nick is a good friend of mine.
INTO JAPANESE
ニックは私の親友です。
BACK INTO ENGLISH
Nick is a good friend of mine.
That didn't even make that much sense in English.