The first part is a "police department policy" question. Some police departments choose not to involve themselves with 17-year-old runaways, because they know that kids that age are likely to keep running away, and in states like Texas the juvenile court probably won't or can't do anything once the kid turns 17. But it's still running away, and as panther10758 indicates your boyfriend can get in trouble for "harboring a runaway" if he helps you hide from your parents. (And you may live in a jurisdiction where the police will make you go home.)