I agree with Antidote, in her first paragraph describing how if you communicate clearly and try to explain and straighten it out (and that has to be by both parties), and it STILL is a problem, then yeah, maybe they don't deserve another chance. I agree there does come a point where you're just asking for it/being a doormat. (I have some experience doing that myself--being a doormat. But not anymore.)
Thank you Cindy for saying that.
As far as your brother goes, he's had these feelings for decades now, so they could be so strong just because time has gone by without anything changing. But how was anything supposed to change when he didn't tell you he was mad or hurt, and, you didn't know how things affected him. There wasn't really an opportunity to clear anything up. Since it happened in your childhoods, you were not really responsible for him, so you cannot hold yourself responsible because you were trying to survive also. He obviously saw you as more than just a sister even tho you weren't his parent. Anyway, I'm sure you know all this....Have you talked to him about it? Have you apologized for hurting him? And leaving him behind? (NOT saying you're guilty, but there's nothing wrong with letting him know you feel bad that it hurt him so much). Have you ever been involved with each other's lives as adults? Actually I'm no expert on siblings. I've been estranged from my sister for...ever. Some things aren't repairable but not if both of you want to try!
All you can do is show him how you feel bad about not being aware that he was so hurt by you leaving, and then the ball's kind of in his court. I hope he can see you never had any bad intentions toward him!