YOU SAID:

because he thinks he's just a friend to me

INTO JAPANESE

彼は彼が私にとってただの友達だと思っているから

BACK INTO ENGLISH

He thinks he is just a friend for me

INTO JAPANESE

彼は私の友達だと思っています

BACK INTO ENGLISH

I think he is my friend

INTO JAPANESE

彼は私の友達だと思う

BACK INTO ENGLISH

I think he is my friend