Woman's sister invites boyfriend she's met twice to live with them, 'I'm in the Twilight Zone.' AITA?

"AITA for fighting with my sister because she invited her boyfriend she's met 2 times to live with us?"

I never thought I would post anything, but I feel like I'm in The Twilight Zone and want some outside perspectives. So, some background, I (32F) live with my sister (29F) in the home she was able to buy with inheritance from our father passing away (I used mine to complete my master's degree in counseling).

We've both been having a hard time financially. My sister has been going to nursing school, and has been working less. Because of this, I have covered her mortgage and the majority of the bills for nearly a year and a half now. I think our arrangement is mostly equal because she is also helping me get to work since I don't drive.

My sister has had a string of bad relationships and has always been impacted by any sense of rejection because she has borderline personality disorder. Despite my training as a therapist I've always really struggled to set boundaries with her or have calm conversations about things that upset me regarding our living situation. Once she makes her mind up, it's impossible to change it.

Now here is the current situation. My sister has been actively dating again despite some disappointments. With the most recent guy, after their first date (and talking for a day or so), I heard all the things I've heard before. That he's different than the guys she's met before, and she thinks he's the one.

I've heard this 4-5 times, all of which ended messily, a pattern that I would no doubt draw a client's attention to, but I'm not my sister's therapist. Anyway, a couple days go by and I start to notice she's moving even quicker than is typical, confirming their committed relationship after one date and a couple days talking via messenger. I notice, but keep my judgy comments to myself.

Then she goes on their 2nd date and I get a text message at midnight informing me that he's going to be moving in with us because he has nowhere to go. There is no discussion, and no chance for me to voice my agreement or disagreement. She has decided, and I am just being informed of her decision. She acts confused when I am angry about it.

I hate living with roommates, I can't move out easily, and she does not actually know this person. During our fight today she said that the reason she said yes is because she doesn't want him to go back to the place where he was addicted to substances, which is not a ringing endorsement. She says it's her house so she gets to decide, but my point is, I have been paying the mortgage and bills for months.

I think I should at least get a say in the matter. It is her house, and she has helped me a lot, but I think it's basic respect to care about what I have to say about it. We had a really awful fight, and I shouted that I would move out and not pay the mortgage for this upcoming month.

Having calmed down, I have decided to still pay the mortgage and told her that. I might still move out, though I don't know where I will go. She says I don't have a say about him moving in and that I'm trying to control her. Am I the ahole?

Here's what people had to say to OP:

goatmom5 said:

NTA You need to move out. If you can afford her mortgage and bills, you can afford your own place. Sis needs to stand on her own feet and feel the consequences of bad decisions. No more bailing her out. She's an adult.

Smarterthanuthink867 said:

NTA. You not wanting him to move in there isn't being controlling. She barely knows this man. Stop paying her mortgage. Save your money and get your own place ASAP.

Acceptable-Law9406 said:

NTA. I can tell by the post that you are genuinely concerned for your own safety. It would be best for you to move out as soon as you can. Since your sister's name is on the deed, it's her responsibility to pay the mortgage after you are gone and paying rent on your own living space.

AvocadoJazzlike3670 said:

YTA to yourself. You have been paying mortgage and she gives you rides and you somehow think that’s fair?!?! Girl no it’s not fair. It’s her house then stop paying the mortgage.

MontanAngel said:

YTA if you stay living in this house. Do not pay any more bills and move out and get an apartment or studio within walking distance or bus distance to your place of employment. She herself told you to get out so follow her advice and leave.

NoPhone4571 said:

NTA, and you need to get out ASAP. She doesn’t know this guy, and I’m pretty sure you’re going to get home from work one day to find the house cleaned out.

ElaraMarie said:

STOP paying the mortgage! You definitely should move out and put that mortgage payment towards a place for yourself. She is blatantly disrespecting you and all the help you've given her. BUT...it's her life and if she wants to f it up by letting a strange man move in then it's on her. Luckily for the sister, he can get a job and help with the mortgage now!