I know this is not a dating post. However, this is the only platform where I can be assured that people will not give my brother the benefit of the doubt. Even 2X can't assure me of this.
My brother has the tendency to be pushy, possessive and dishonest a lot. In a nutshell. In front of people he seems restrained and intelligent and people think he's a decent person. He is not. I even tried to tell someone that I can't stand my brother (especially in light of my dad passing away) and the person (a woman!) said "Oh stop! He's your brother." People like her are going to be my downfall.
I feel as if I can't talk to anyone who has already met my brother because if I tell them that he's not the same person that they all think he is, they won't believe me - even the women. This is bad. He's not to the point where I need to "go to a shelter" or get a restraining order YET (although he does call and text excessively even when I tell him to please not to) but who knows, what if it does get to this point? He claims I've all he's got left and that he can't lose me.
I can relate. My mother is a bit similar to your brother. In public, she's all sweetness and light but behind closed doors, she can be a monster. I've opened up to many people about my mother over the years but not one has ever believed me because she's such a good actress.
One thing I've come to realise though is that, I know the truth. Even if no one believes me, it doesn't change the truth. There's comfort in that. I've also stopped venting to people IRL about it because most people IMO are unwilling to believe that a family member can be abusive. I think people would rather believe that all families are loving and kind because believing that is much more comforting than accepting that sometimes families can be dysfunctional and abusive.
He claims I've all he's got left and that he can't lose me.
That's his problem, not yours. You're not obligued to put up with abuse from anyone, not even family members. Also, if he were genuinely worried about losing you, he'd treat you better so you wouldn't leave. Please don't fall for this emotional blackmail.
For what it's worth, my advice is to try and become as independent as you can i.e. get your own source of income and your own place to live, and then you can have as much or as little contact with your brother as you like.
I went NC with a sibling. You can too.
Cut him off if you can. I also have a narcisstic brother. It boils down to his looks and society always propping up men. Chances are he isn't even that secretive. People just excuse ill behavior in men. especially if they're good looking or "the life of the party".