Boyfriend sister problems 🤬

So my boyfriend for 6 years sister just unfollow me on Instagram because I told her I could not mind her kids I have to go to work. So turns it around tells my boyfriend I be rude to her and her kids I don’t let them do what they want. I try telling my boyfriend that she’s lying I told her I can’t watch her kids because I was going to work. Now my boyfriend and I never had an argument in our 6 year relationship until now. I don’t complain when she brings 7 bags of clothes to wash at our house or that she have a key and come use up the light and eat what’s in our fridge. I was not invited to her wedding last year or even her baby shower that’s next week. Don’t include me on the family trips and honestly I blame my boyfriend because he supposed to stick up for me. When they ain’t ask me why I don’t come to they events his sister yells out she don’t want to come and when I try to tell the family I was not invited she talks loudly so they can’t hear me.

What would y’all do if this was y’all?

I been very patient and understanding since they mother passed away 2 years ago but I can not take his sister behavior anymore and I feel like my boyfriend is in the middle.