Am I the Asshole?

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The original was posted on /r/AmItheAsshole by /u/Accurate-Panic-1639 on 2023-07-18 21:10:44.

I 24M been dating 23F for about 4 months now, I just met her family about 1 month ago, everyone but her older sister 30F since she lives out of town.

This weekend, my girlfriend was staying over at my place, i live by myself in a nice quite big loft and do pretty well for myself financially, my place is decorated with my interests like gaming/books/photography, so it has a lot of stuff that breaks, so i avoid visits when possible.

This weekend her older sister decided to visit town with her kid 7F, older sister is a single mom and the father is completely out of the picture, girlfriend on Sunday asked if her sister could come over, since she wanted to see her but didn't want to leave our planned weekend together, i said sure since she promised it would be a quick visit.

Now i don't dislike kids, in fact i tend to quite enjoy being around them but my place is definitely not kid friendly, so when i opened the door and saw she had brought her daughter i wanted to turn them away right then and there. But for the sake of my love, i welcomed them in. They chatted a bit in the kitchen while i was getting everyone's drink. That was until 7F realized Minecraft was on the PS5 (my girlfriend was playing) and started to scream at the top of her lungs she wanted to play, controller was in girlfriends hands, so sister saw that and asked if she could let her niece play for a bit, girlfriend looked at me and i said no, sister replied saying she asked girlfriend not me, to which girlfriend replied saying that she was in my house and it was my console so i answered regardless of who she asked.

She started going off about how it's she can't afford to buy games for her daughter and how hard is being a single mom, basically screaming at gf and me at which point i told her "it's not my fault you decided to open your legs to a deadbeat, now get your kid and leave" which was received as well as you'd imagine, girlfriend had to almost physically shove them out of my place and has since started getting texts from her whole family demanding she breaks up with me and saying it's appalling "the way she let me treat her older sister", girlfriend doesn't think i'm the asshole but said i could've been more diplomatic. AITA?

Edit: title says son but it's a daughter, got confused and can't change it now, sorry.