His family is not your family, if he’s wrong they’re going to be on his side, same as if he’s right, they’re gonna be on his side. Never vent to your family, they love YOU, not him. Meaning that when you forgive him, they won’t.
His sisters are just that HIS sisters, & his brother is his brother. They’ll smile at you, & at the other girls. To them? Every girl he takes home is their “sis in law”.
Oh & Lastly, never let your friends know when he messes up, you’ll forget about it, they won’t. Good Luck. In other words keep what goes on in your relationship quiet…. Don’t talk to much…..