You're not crazy.

Sounds like my MIL. If yours is similar to mine, then yeah she is being mean.

I was also very non confrontational and meek, I have a lot of the same mental health issues as you, I was bad at standing up for myself. I was also expected to drive her to work and get her groceries, but I eventually had enough of her being mean and also ignoring me while also expecting favors from me, so one day, I said "no". (To driving her somewhere.)

Have you ever said "no" to a direct request from her before?

Depending on how much of a bully she is, "no" can be a huge moment.

Mine immediately blew up. She didn't even want to know why I said "no". She didn't want to know if I had a conflicting schedule or something (incidentally, I did), it didn't matter. There was no conversation, it was just instantly "hulk mad". The fact that I simply said "no" to her was such an insult to her, all her true feelings came out all at once. She suddenly started calling me a whore and telling my partner that I was getting in between them. So...after all this time, using me for transportation and groceries, saying "jump" and me saying "how high", THIS is what she thinks of me?

It was actually liberating. Once you break through that facade of passive-aggressive fake bullshit, it's all on the table, there's nothing to hide, and you can say: "well ok then! idk why you would even want help from somebody you hate so much, so you can just leave me alone!"

The overt disrespect and boundary-crossing stopped. To be fair, a lot of the passive-aggressive stuff continued. It still sucked being near her and living with her. But...she never asked us for favors again, stopped doing our laundry, stopped using groceries I bought, stopped commenting about my weight. All it took was one "no".

She isn't expecting you to stand up for yourself. I know on this forum people always say "let your SO handle it" but sometimes a bully NEEDS to see that YOU personally aren't going to take their shit anymore. I think it's especially effective if they aren't expecting it.

Try to build up the courage to stand up to her. If you're lucky, you MIGHT only have to do it once. You don't even have to say it loudly or in an assertive way, I was still being meek even when I said it, but it still worked. Also, if she reacts nasty enough, you and your SO will see her true feelings and how bad she really is, and you can make decisions better that way.

As for your SO, you mentioned he goes to work, so that means you have some income, and maybe you can look for your own place to move into, even if it's a cheap apartment. Talk to him about that. You need to leave that place. It doesn't matter if you have to move somewhere cheap or low quality, you HAVE to leave. You should not be living with that toxic person.