AITA for living with my cousin of opposite Gender in a 1 bhk apartment?

I'm 24M, girlfriend 24F, my female cousin 22F. All of us are working in IT.

Till now, me & my girlfriend were living separately in respective 1 bhk apartments. We've no plan to marry within 2-3 years and no plan to live together before marriage.

It's the capital of our country, rents are too expensive, eat up around 30% of my monthly income! I was living alone in that apartment till now.

My cousin recently got a job here. Soon, we decided to live together in my apartment and obviously split the rents. Both of us share a very healthy & close bond since childhood. The fact that we both like to live neatly & organized makes it even better.

It's a win-win situation for me & my cousin as it's saves a HUGE part of our income and we get each other's company at home. For me, it's not a thing in which I need my girlfriend's approval, as we aren't going to live together for at least 2-3 years.

I told it to my girlfriend before 6-7 days of my cousin's arrival. She gave me an unexpected reaction and said that it's weird that 2 grown ups of opposite gender live together with no romantic interest in a 1 bedroom house. Basically, inappropriate. I found it honestly gross that she's sexualizing a brother-sister type relationship. My cousin is a part of my family. Our dads are real brothers!

Please note that the bedroom got 2 separate beds installed. It's been nearly a month, we're living together happily and it has made life easier in every way. We even divide the housework, which reduced my overall workload. So I'm in NO mood to change the things just because my girlfriend is being uncomfortable, AITA?