Living with someone can quickly get complicated when a third person suddenly shows up.

In this story, a woman was living with a roommate with whom she was getting along pretty well.

But when her roommate started dating a guy and inviting him over, everything quickly changed.

Read the full story below for all the details.

AITAH for telling my roommate that I refuse to pay 50% of the rent now that her boyfriend has moved in.

I’ve been living with my roommate for almost three years.

We get along pretty okay. We both keep the shared spaces clean.

Sometimes, we cook together and watch TV in the evening.

Other than that, we don’t have a whole lot in common.

This woman’s roommate started dating a guy.

I moved into the house and met her for the first time then.

A friend of a friend knew I was interested in moving. They introduced us.

About four months ago, this all changed. She started dating a new guy.

Even though he has his own place, I see him here all the time.

Practically every day.

She thinks her roommate’s boyfriend is very condescending.

Sometimes, I come home from work. He has let himself in even though she’s not home.

So I think he has basically moved in.

To be honest, I don’t really like the guy.

He teaches kindergarten. He uses this specific voice on me.

It sounds like he’s talking to really little kids.

I think he’s very condescending.

She noticed that their monthly utility bills have increased.

I’ve also caught him using my pots and pans to make food, even though he cleans them.

I didn’t say he could use them.

Anyway, I had an argument about a week ago about the rent.

I’ve noticed our utility bills have increased. It’s definitely because of this guy.

She decided to pay only 33% of the rent.

In the past, I give her cash for my share. Then, she Zelles the landlord.

This month, I only gave her 33%. She flipped out.

I said to get the other third from her boyfriend. I said he lives here.

I don’t think I should pay half anymore.

But her roommate thinks she owes more.

She said that because he lives in her room, he could consider kicking in for her rent and not mine.

She said that she might sue me. She said I owe more rent.

I don’t think so.

AITA?

Let’s check out the comments of other people on this story.

This person makes a valid point.

Here’s another sensible insight.

Your roommate is overstepping big time, says this one.

Here’s some sound advice from this user.

Finally, another quick suggestion.

When a third roommate moves in unexpectedly, the math won’t add up.

If you thought that was an interesting story, check out what happened when a family gave their in-laws a free place to stay in exchange for babysitting, but things changed when they don’t hold up their end of the bargain.