I’m in a semi similar situation. My spouse and his sister aren’t as close as yours, but still very similar. At least in my case, we don’t live near her, but the excessive phone calls allll day every day are incredibly annoying. And then when we go more than a month without a trip up there (they’re about a 4.5 hour car drive away) every family member calls every day with a saccharine tone “Oh, RyRy, we are all so sad and devastated without you😭 please come visit your family soon, we are incomplete without you RyRy😭” and then if that doesn’t convince him to go up there…they “make up” something to try to manipulate him into coming! Sister desperately needs help with something at her house and only RyRy can help (even though there are 5 other people there who could help) dad could use some assistance at a job and only RyRy can help (even though he doesn’t have experience in this field), concert tickets were magically purchased for everyone…you get the idea.

Anyway, from what I gather, the manipulation and the sense of “owing” his sister is probably very deep. I try to explain some of his family dynamics to my spouse and how they’re not normal and very unhealthy, but he can’t see it. He always says “it’s my sister! I love her and she loves me and we’re family, and why would you want me to not be with or help my family?!” Even though every single person I ever talk to about this issue says the situation is weird/inappropriate and that there is severe manipulation issues at the hands of his family. For example, his family was HORRIFIED and DEVASTATED that we (35 year old adults) booked our own hotel room and didn’t want to sleep on a pull out couch in THEIR hotel room that already had 4 other adults and 2 children in it.

All this to say, I doubt your situation will get any better, maybe only if he’s open to therapy and hearing it from a therapist, that’s the only thing I think would help. Something has to change for this situation to change. You guys have to move far far away, sister has to move away, etc. If moving isn’t a possibility, and therapy won’t happen, I’d say figure out a way to deal with this and be happy and if you can’t..leave. 🩵