Your brother is who he is. Nothing you do will change that, and your girlfriend couldn't be more right.
My "ex-brother", as I like to call him, tortured me when we were kids. He's 7 years older than I am, so you can see he was twice
as old and twice as big as I was.
I asked the dips**t for an apology when he was 53. You know what he said? "I'm not going to apologize for being a kid!" Yeah; way to show some maturity, huh?
Fantasies do no harm; they're only a problem if they're acted upon.
I found therapy to be very helpful in order to regain not only my self-respect and self-esteem, but to get my personal power back and not let his issues run me down.
When our mom died 5 years ago, I was able to brush him off, and it won't be too soon if I never see, or hear from, again. I encourage you to do the same. It's a real boost to the self-esteem!