like a brother/son/father/sister/mother/daughter to me

Like a brother/son/father/sister/mother/daughter to me is the phrase often used when you want to tell someone how close they are to you and how they feel like family. By saying they are like your brother, sister, mother, father or other family member, you are saying they feel so close and so familiar to you that they feel like family. It is also often spoken about someone who seems to have a lot of the same traits, opinions and mannerisms as you and therefore feel related to you.