he is a friend of me 这是不正确的表达
he is a friend of mine 才是正确的,等于 he is one of my friends.
他是我的一个朋友嗯he is a friend of my father是不对的 He is a friend of my father's 才是对的, 等于 he is one of my father's friends. 他是我爸爸的一个朋友