WIBTA If I move out of our apartment knowing my fiance and his mom can't afford it without me

Throwaway b/c my fiance follows my main.

Me (F29) and my (ex?)-fiance(M27) have been living together for about 1.5 years. Fiance got his undergraduate degree, worked for a couple years and then decided to get an MBA which is how he ended up in our city. We moved in together after he finished his MBA program. Fiance is from the mid-west and his mom has always wanted him to move back. When he told her he was staying here she was heartbroken.

I went to college and got my degree in a STEM field. After I graduated, I got a job with my current company and moved to the city where we currently live. It's a big international company with multiple locations in the US and international. I love my job, I like the company I work for, and the pay is pretty good. All in all, a pretty good deal. During covid my office shut down and we all went WFH. After covid they decided not to reopen this office so I've been 100% WFH since early 2020. I currently make considerably more than him - mainly because I've been working for 7 years and I'm in tech.

I had been living by myself in a one bedroom apartment and just had my office set up in the living room since it was just me. When we moved in together, we decided to get a two bedroom apartment so I could use the extra room as an office. Because of this I was paying 2/3 of the rent and he paid 1/3. We split everything else 50/50.

So the problem started this past May. Fiance's mom told him she wanted to move to our city to be closer to him. She asked if she could stay with us while she looked for a job and got settled. She's a teacher so figured she'd be able to get a teaching job pretty quickly. Because of that I didn't really mind her staying with us as I figured it would just be for a couple months over the summer. Since I thought it would only be for a couple months, I moved my office into a corner of our bedroom and fiance bought a bed to put in the 2nd bedroom. The problem is she never applied for any teaching positions and has been living with us for 6 months now.

She and I have really been struggling with each other since she moved in. I can't make her understand that I work full time. She constantly interrupts while I'm working, which is bad enough but she even interrupts when I'm on Teams calls. She always asks me to take her places bc she doesn't like to drive in our city. She has pretty outdated views of gender roles and is constantly giving me a hard time for not doing more around the house and making Fiance help with chores, do his own laundry, etc.

The constant critisism and insults are just really wearing me down. And I HATE having my office shoved in a corner of the bedroom. Back in September I told my Fiance that since it looks like his mom is going to stay awhile we should split the rent 3 ways. He told me she can't affort that since she has to conserve money until she gets a job. I told him I wasn't happy paying extra for a bedroom I can't use so finally he said we could do a 50/50 split. I could afford to pay the extra, but I hate the idea of funding her lifestyle.

Everytime I complain about her or the situation he says he agrees but doesn't know what to do becaused he can't kick out his mom. And he won't talk to her about the way she treats me or how she behaves. When I ask what the longterm plan is, he just says he doesn't know. I've thought about giving him an ultimatum to tell her she has to leave, but I think he'd just end up resenting me for essentially putting him mom on the street.

So one of my girl friends is losing her roommate the end of February. Our lease renews June 1st. I'm very strongly considering moving out of our current apartment and moving in with her. I can afford to pay my part of rent on our current apartment and also half the rent at my friends apartment. It's not ideal but I'm not a big spender so it's doable.

The issue is - If he and his mom aren't able to pay for 1/3 the rent each, there is now way they could cover the whole thing on their own. But I can't live like this anymore, so I'm pretty sure this is what I'll do but I wanted to see if people thought I'd be the AH for leaving them like this.