AITA for wanting to confront my sister?

AITA So my older sister(26) was dating this guy from California(24) and he moved here. He cheated and they broke up and I was at her side every time she needed me. She got back together with him and he wasn’t a horrible guy. I understand what he did wasn’t okay but my sister is a diagnosed sociopath. Well they recently broke up again and she doesn’t have a job so he has been still paying for all the bills while she messes around on vr. Two nights ago she asked me to take him to the store at 9 pm so I went and I picked him up. I was kinda sick and I needed to get medication anyways. We go to Walmart and she has this hugeeeee list and so I had him send it to me so I can put it in my notes app and mark it off as we went. Took almost two hours but we got everything. We put everything in my car and I’m talking to him about my sister. Apparently she doesn’t even help him carry the groceries in after doing that for her. I take him home and he goes to unlock the door while I start grabbing things to carry inside. She doesn’t even acknowledge his existence. I go inside to put things down and she’s playing on her computer and says hey to me. I finish helping carry everything inside and I use the bathroom. I go to leave and I give her a big hug and she thanks me for taking him. Mind you she didn’t even thank him for spending $217 on groceries for her weirdly specific items she wanted. She’s always yelling at the poor guy. I just think he deserves a lot more than that. I know he cheated and all but no one deserves to be treated like that.