My Sister Abuses our Relationship
This is a very sad situation. Here you are in your 50s and your sister doesn’t treat you well. Unfortunately, you care more about the relationship than she does so she continues to get away with it. I suspect that you’ve already tried to talk to her about what she does to you but without effect. If you haven’t done so, then it’s at least worth a try to talk with her to figure out what sets her off. But if you’ve done the talking and she isn’t changing, you really only have two choices: You can take your distance and mourn the sister you wish you had but don’t. Or you can find some way to let her be who she is without letting it hurt you.
I suggest the latter. She has been doing the same stuff for years. Nothing you say or do seems to change it. It’s just who she is. The next time she lashes out or cuts you off, you could take the attitude of “there she goes again,” shrug, and go on with your life. Her spells have nothing to do with you. She always comes back around. Just be glad to see her when she does, enjoy the good times, and let the rest go.
I wish you well.