Siblings of those with bipolar

I (27f) try to remain close with my sister (22f) who has bipolar and schizoaffective disorder, but sometimes her anger and emotional outbursts make it really hard. She’s currently on disability and unable to work, and when I vent about my job she gets upset and says I have it easy while she struggles.

I let her stay at my place often because our home environment isn’t great for her, my parents struggle to support her and my older sister has her own issues (alcoholism)that create conflict between them. She puts me in the middle constantly and wants me to take sides, which is exhausting.

The hardest part is that I need alone time, but when I don’t bring her back to my apartment after work she acts like I’m abandoning her. She also resents what she calls my “perfect” life, even though it really isn’t. I don’t have many friends outside my family so it’s always just been us, and I genuinely want to support her, but it’s becoming too much.

Has anyone else navigated this? How do you set limits without feeling like a terrible person? Also, how do relationships with your siblings end up in the long run