Yep ANOTHER day where I get to sit here and listen to my mother rock in her squeaky rocking chair all day while do nothing siblings get to go on with their merry care free lives. I KNOW I'll never REALLY get over the resentment I have for certain siblings, but how do you get past the Anger ??
I dealt with it in two ways. One, going into therapy for a few years and two, pulling back from the situation and finding someone else to take care of my mother. (Not a family member). I see my mother once or twice a week now at most. I'm no longer at her beck and call, and I get sufficient time away from her to decompress.
Your situation would drive me berserk! Maybe you need to have a heart to heart talk with your husband, and make clear that without a whole lot more support from the rest of the family, you're no longer prepared to be the caregiver for his mother. That's what I would do in your place. Wishing you the best!
Now, if SIL begged you to take in her mother and promised to help you and now she isn't living up to her promise, go ahead an resent her. Shut her out of your life if you want to. But resenting her because she made a different decision about her mother than her brother did just doesn't make sense to me.
You need help. You need breaks. You had hoped you could et that from your good friend SIL. Oops. That didn't work out. Disappointing, but you still need help and respite. Arrange that. Pay for it with MIL's funds. What would you do if your husband was an only child?
I am very glad you are going to get some therapy. The energy you are wasting on nonproductive resentment could be used for better things!
I personally don't believe in unchosen obligations, including the supposed obligation of adult children to care for their parent. Unfortunately, though, there is often no other way to provide for the parent's needs. In that situation, I think people who care about one another will try to allocate the burden as fairly as possible. That's what I do, and that's what I expected my close siblings to do. I would love to be living out of state and see my mother only occasionally, but I wouldn't place that burden on the remaining caregivers (my one sister and my mother's live-in helper, who is a good friend of mine).
I don't blame Struggles for expecting more from her SIL. I suspect that if Struggles decided to stop caring for her MIL, the loudest objections would probably come from SIL, who is depending on Struggles to keep doing it all so that she doesn't have to do anything. Maybe that's incorrect, but that's what happened with my eldest sister/former BFF when I tried to cut back on my involvement with Mom. In her book, she was free to decide not to care for Mom, but I was not. That does not seem like it could possibly be right, to me.