20. Their Family Has Adopted You
Every time you ring up your own family they'll undoubtedly ask after your best friend, "how is she getting on? Is she still seeing that boy? What does she like to eat so I can get it in when you two come over for dinner tomorrow night?" In fact, you probably suspect that your family prefers her over you in secret, since they don't actually ask you the same sort of questions. And it's always extremely humbling to be invited over to your best friend's house for Christmas - that's how you know when you're truly family. Because that's basically an invitation to then eat them out of house and home.