So, you have a great girlfriend. Excellent! She's smart, she's beautiful, you love her family, and you get along really well with all of her friends. Well... except for that one guy, who's always kind of giving you the stink eye, and with whom she texts back and forth every night right up until bed. Yeah, the one who all but ignores you any time you're all hanging out. You've asked her about him multiple times, but you're always met with the same response:
"[Insert name here]? He's like my brother!"
If a girl ever hits you with this line, or a variation thereof, you should definitely, 100%, without a single doubt in the world, WORRY.