Is OTHER wrong in the post ? POST : Hi all,

I'll try to keep this brief.

I had a big fight with my partner over letting her little sister live rent and bill free with us for 2/3 nights a week every week.

Back story is that rent is expensive where I live and I pay 60% as I earn quite a bit more than my SO.

It's a small 2 bed place and having my own space is important to me.  The second bedroom acts as an office / wardrobe / guest bedroom.

My SOs little sister works in the city we live in and stays with us several nights a week without contributing anything towards our expenses even though she earns reasonably well.

She's also particularly useless when she stays over in that she never cooks or cleans and creates work for us because we have to clean her sheets for other guests and tidy up after her in general.

This drives me crazy as I can't help but feel like I'm being taken advantage of. It's made worse but the fact that my SO never has money for herself and is living paycheck to paycheck. 

I don't want to cause a rift with my in laws so I don't address little sister myself, but I feel my SO should be doing this.

Anyway last night I had a go at my SO about letting her little sister walk all over us, invading our privacy and generally taking advantage. Needless to say, it didn't go down well and Valentine's day is ruined.

AITA?

Thanks for the replies all, I forgot to add that SO and myself have discussed this previously and she is aware that I was frustrated with how things were going. That said, I let it slide for awhile so she may have forgotten how I felt. Little sister is a good person, just oblivious to how her freeloading is causing tension for us.