First, some context – I (36M) have been living with my roommate (32F) for 4 years. We share an apartment because the cost of living in my city is high, and besides, it just worked for us until now. Our apartment has three rooms – I occupy the largest bedroom, and she has the small bedroom plus the living room (which I also have access to but don't use – it only holds her stuff and she decorates it however she wants). We arranged the split this way because I work from home and needed a room big enough to set up an office as well. I'm also a homebody, so I really value my own space and spend a lot of time in it – I only leave the house for grocery shopping, dates, and jogging. She, on the other hand, spends most of her time out – she works in the city for 10-12 hours each day and is very outgoing; she doesn't like staying in and often goes out with friends.
I am in a relationship with my girlfriend (33F), who visits me regularly, about twice a week, and sometimes stays the night. We plan to move in together once our life situations stabilize a bit (I don't want to get into details here, as they are irrelevant to this post). My roommate was single for most of the time we lived together, but a year ago she met a man (34M) from another country online, and they are in a long-distance relationship. During this time, they have seen each other in person once, when she visited him in his country.
Recently, a conflict arose between us because her boyfriend decided to visit her for 10 days and, by default, stay at our apartment. I didn't mind this. However, as the arrival date approached, my roommate started asking if I was planning a vacation or a trip during the time her partner would be visiting, which was in July. I answered truthfully that I had been on vacation in June and had trips planned for August and September, so I wasn't planning on leaving the house in July. Especially since my work is freelance/contract-based, and when I'm not working, I simply don't earn money – for this reason, spontaneous trips are out of the question for me. I have to plan everything in advance to manage my finances well.
My roommate acknowledged this and didn't bring up the topic again. Until recently. A few days before his arrival, she asked again if I was planning a vacation while her boyfriend gonna be here. I answered again, though a bit annoyed, that I wasn't – I had already told her before that I couldn't afford a spontaneous trip and needed to work more this month. She didn't comment on it and walked away. The next day, however, she started the conversation again. She told me that because of me, she had to rent an Airbnb for 10 days to stay there with her boyfriend, and she believes I should pay her for it because it was because of me – since I refused to leave the apartment. She told me that she was "forced" to do so, and it is a significant burden on her budget.
I told her she must be joking and can forget about it. I also mentioned that she didn't have to do anything, as I had no problem with her boyfriend staying with us during his visit. She replied that they needed privacy and my presence at home was unwanted, so she had no other choice.
When I told her I wouldn't pay for her choices, she changed her tactics. She said that since my girlfriend visits regularly, she should contribute to the rent because it's as if she lives with us. I told her that was out of the question too, and that my partner only stays over a few days a month – she is a guest, not a resident. This angered her again, and my roommate claimed that she was suffering financial losses because of me.
Finally, she brought up another argument in the heat of the fight. She said that since I have a larger room, I should pay more (even though during the initial renting and every annual lease renewal, she was always fine with a 50/50 split, especially since we also agreed she could treat the living room as her second room). I told her that if she felt that way, she should have said so at the time of renewal (in February) – then we could have renegotiated the rates. However, I stated that as long as the old agreement with an equal rent split is in place, I have no intention of paying her anything extra, especially since she had absolutely no problem with it for so many years.
Seeing that none of her attempts to stick me with the bill for her meeting with her boyfriend worked, she said she thought "we were friends" and that it wouldn't be a problem for me to do her a "small" favor. She said she was wrong about me and that I turned out to be a classless person.
My partner and all my friends I've vented to about this situation say I have every right to live in the apartment I pay for and that my roommate is completely overreacting. Still, I'm looking for validation from people who have no personal connection to me. AITAH?