My (28F) Husband’s (29F) Best Friend (23F) is Ruining Our Marriage and Driving Me Insane

I want to preface this by saying that my husband has autism, his best female friend has ADHD, and I suffer from childhood trauma and depression.

My husband (29M) and I (28F) have been married for almost 2 years now, together for 4 years. He met his current best female friend (23F) at work, they've been friends for about four months now. She has lived a sheltered life because her family is extremely religious so they home schooled her and she didn't go to college. She's still very childish and doesn't know how to be a functioning adult, especially since she still lives at home with her parents and they control almost her entire life. My husband felt badly for her because no one in their department can stand her so he's taken her under his wing and she never leaves his side.

I started working at my husband's company three months ago in a different department from the two of them, which was when I met her. My husband really wanted the two of us to be friends. So he volunteered me to teach her how to drive (he doesn't have his license) and made us all hang out once if not twice a week in addition to all of our breaks at work. For the past month, she's also been staying with us 3-4 nights a week (not really a decision I was included in but instead informed it was happening) on the living room couch bed so we can drive her to work (her mother is disabled and her father has a new job so he can't drive her most days). So at least five days out of the week every week, it's the three of us. Then the other two days my husband and I are too tired from work and chores.

At first, things were mostly fine. Some days she's okay and will be decent towards me. However, 50-75% of the time she'll glare at me, talk under her breath in response to something I said or did, interrupt me whenever I try to speak, and actively get in between my husband and me. She's extremely touchy feely with my husband, which he claims she's like with friends but she's not like that with me at all, a supposed "friend". She also had made promises to my husband prior to her staying over she hasn't kept. She promised she'd wash any utensils or plates she used (she's done none), that she'd buy her own groceries (she buys cheese and fruit, then complains it's not enough for dinner and eats our food), and that she would just be all around respectful (except she chucks her trash everywhere and has never cleaned any of it up, neither has my husband, so it's been my job).

My husband thinks I'm overreacting and that all of her behavior is innocent, I'm just viewing it through a malicious lens. He says there's no way it's malicious because she tells him how much she likes me and how much she enjoys spending time with both of us even though she never likes spending with other women.

Regardless, sometimes he claims he doesn't see the behavior that happens literally right next to him, other times after the fact he'll say he had noticed how she was acting towards me but didn't know how to do anything about it so did nothing. He initially thought a few weeks ago it could have been malicious but since he's found out she has ADHD and treats other people in their department similarly horribly, he thinks it's just because she's mentally ill and I need to accept it.

None of this behavior has ever been directed at him though and he made sure to tell me he has never had any negative interaction with her (funnily enough, he said that while we were having an argument about her impact on me, which really hurt). I keep trying to be her friend. I go out of my way whenever I can to get things for her, to help her feel comfortable at our apartment, to listen to her problems and offer advice when I can, I'm doing literally everything I can to be her friend. Some days it's okay and I think we're making progress. And then the next day I'm treated like I don't even exist or that my existence is literally the bane of hers.

It's killing me. It's driving me insane. It's making me feel suicidal because my apartment doesn't feel like my home anymore, my husband and I fight almost every day, I have to see her all the fucking time, and I'm in a constant state of unbearable stress.

I've talked with my husband on how emotionally draining this is and how suicidal it's making me but he doesn't get it. He's continued to try and force us to be friends by making us spend more time together. He continues to say he'll find a way to "fix" this because he doesn't want to have to choose between us. For the past month, I've had to force myself to be around her just so I can actually spend time with my husband.

I've told him how I don't understand why this is such an issue for him. If I had a friend treat him like she's treating me, I wouldn't want them as a friend. I've talked about how I don't understand how a friend he's had for 4 months who treats me like shit is being treated equally to me, his wife, the supposed love of his life.

I'm losing my fucking mind and I don't know what to fucking do.

How can I get my husband to understand how seriously this is affecting both me and our marriage?

Tl;dr: My husband's female best friend with ADHD treats me horribly 50-75% of the 5 days I'm forced to spend with her each week and my husband doesn't really see a problem with it, other than my perception of her actions.