Background: Me and my boyfriend of 5 years just moved to his hometown this year. We just had a baby. She’s now 3 months old. He has family that lives here

He has two sisters and one of them is 20 years old with autism. This week he has been taking her back and forth to work since she has no other way. Her dad works during the day so she’s left at home by herself and she can’t drive. Her work is a whole 40 minutes away. This morning she was spamming his phone with texts and calls because he didn’t know he was supposed to take her into work this morning. His sister and his dad never asked him to take her in this morning. It was just expected of him. We were up with the baby about all night last night. We’re freaking tired. She called him yelling at him and I got pis*ed and told him if she’s going to act like that I wouldn’t even worry about taking her. She even woke the baby up with her calls. I told him he needs to learn how to stand up for himself and he needs to learn how to say NO. He’s way too nice and it leads to him getting stepped all over. He said he’s only doing this favor for his dad because he feels like he “owes him” since his dad never asks anything of him but he always asks his dad for things. But it’s still so frustrating to me. I told him that his sister being autistic isn’t an excuse to treat him like sht. He just shrugged his shoulders. AITAH??