What would happen if you ignored sister's behavior completely and didn't let her put a triangle in your marriage by fighting H about it? You are so inconsequential to me that you can lie to my H all you want for years and I don't care. She is baiting you through H and hurting your marriage. He is too dumb and manipulable to ever recognize it on his own. Take away her power. Maybe she'll get bored and try to punish you some other way (like within your family). I don't think you can fix your sis. You can't let your lifelong troubles with her ruin your M. I know it hurts, but let her badmouth you to H and see what happens. Tell him to talk to her all he wants, who cares? Just not to tell you anything more about it because it is of no interest after this point. Then live it out and never listen and never ask. Word will get back to her after a year and she might lose interest in her IM friendship with your H.
That is one long-term view plan. I'm not saying it would be easy or fair. I'm trying to take the fun out of it for her to help you. Maybe I'm wrong.
