My sister hated my ex-boyfriend throughout our entire relationship. I can see why, to some degree, because he put me through a lot of stuff and there were quite a few times I couldn’t hide my depression about the relationship. In my heart I feel like most of our problems stemmed from him – but – I wasn’t perfect in the relationship, either. It’s also a lot easier for people to complain about the bad stuff more than it is to go on and on about the good stuff. That’s how it was for me. I didn’t mean to do it that way, but it happened. But that’s just it – he wasn’t all bad or the only one who fucked up, but that’s how it seems to my sister.
So like other people have said, you just don’t have any way of knowing, really. I know that when my sister constantly and openly expressed her hatred for my ex, even during obviously good times in the relationship, it stressed me out beyond belief and made me pull away from her somewhat. I felt like she wasn’t even trying to see things from my perspective or to see the reasons I was with him.
That said, she’s my older sister by two years and I know she’s very protective of me because she loves me. I get it, I really do. But what she needed/needs to understand is that it’s my life.
I completely agree with kevbo. Tell your brother how you feel about her and that you’re really concerned for him because you love him. Stay calm, be clear… And then all you can do is drop it. Do you know this girl, outside of possibly meeting her a few times? Maybe, at least once for your brother’s sake, hang out with her sometime and see how it goes. You never know… You might be wrong. Or not, but yeah… Not much else you can do.