Knock-off friend

A person that isn't treated as anything, but acts the role of being a friend.

When someone isn't regarded as a person, who's feelings are ignored, and who's job is to listen and simply be here because you want to.

Someone who's only purpose is to be a helping friend, but is ignored, mostly emotionally, like they aren't even someone.

Person A: "Who's that guy over there?"

Person B: "Oh, he's Person C's friend. He doesn't really say anything and is only here when Person C needs help. No one really pays attention to him since his only role is to help and not be an actual person."

Person A: "Oh, so he's a knock-off friend."