how much privacy do you expect from those who know about your diagnosis? (venting/advice request)

Overhearing people talk is not eavesdropping. Listening more closely because the conversation is a break in your trust is natural, if they try to pull a "but you were eavesdropping!" tell them if they want a private conversation then to have it in a private place, not a communal area in earshot of the hall outside your room.

Did you make it clear this was confidential, or was it just assumed? If you explicitly told them to keep it secret and they did not, then say just what you said here. You happened to be coming down for a cup of tea when you overheard a betrayal of your confidence. If you are frustrated, let that give a backbone and set a firm boundary, but don't let it put words in your mouth and start saying things that will make them defensive. As soon as someone puts their guard up, the conversation is not going to go anywhere productive.

If you didn't explicitly tell your mom this was to be kept under wraps for now, then lesson learned. You need to have a polite conversation with her and everyone she told that this is personal info not to be shared. Always explicitly set boundaries, assumptions never work, even doctors and therapists sometimes eff up and assume someone knows more than you want them to and spill the beans.

No matter what, your family loves you and only wants you to succeed in life. Spilling your tea was likely done out of an effort to help you in the big picture, misguided or not. For me, once I was comfortable sharing my neurodivergence with my family, life got easier as they were able to take that into account in our relationship. But I understand it's your call, and if you need to come to terms with diagnosis first, that's perfect reasonable and those in the loop should be made aware of how hurtful it is to betray that trust. Nothing a polite but firm conversation can't solve.

I'd like to echo everything Cagi said, and add that it's genuinely possible this conversation with your brother was more of a "they finally got the diagnosis," sort of conversation rather than a revelation for your brother, because everyone probably already suspected you have autism. It sounds like your mother is happy that you have clarity on this and wanted to share your good news.

If I tell my mother something, it's free game for her to tell anyone she knows about it, because she wants to tell other people what's happening with her children. If I don't want her sharing something about me, I could ask her explicitly not to share, and she won't.

Regarding your concern that your brother is going to think you're no longer socializing with neurotypical people, you're waaay overthinking that. You can call up your brother at any time to talk to him if you want to. Next time you want to go visit, almost guaranteed his door will be open for you and nothing will have changed.

I've found out with other things that family needs to be told to keep personal details private from other immediate family. My brother has gotten better about respecting my privacy regarding things like GSM stuff by default, but still assumes similarly queer friends are free to be told (and I believe giving a lot of personal details related to that, not just the label; tbh, I'm actually fine with that, but it still feels like something he should have asked first about).

With autism I'd especially assume no privacy unless explicitly requested because I'd assume people already knew anyways. A diagnosis doesn't really change that.

I had a conversation with a friend about this exact kind of thing awhile back. We realized we had opposite expectations. She was under the assumption that people just kept stuff she told them secret unless specifically told that they could share it. I operate under the opposite assumption: that nothing is a secret unless the person sharing it specifically says not to share it (that applies to myself as well).

Regardless of which assumption one operates on currently, it's much safer to operate under the latter one (I highly recommend it).

Family can be even more complicated, because in my experience even if you tell a family member to keep something a secret, that usually means, to most people, "keep it a secret from strangers" and you can bet that your other family members will find out about whatever it is you told that person.

I mean eveyone in my family knew telling my mom something was akin to telling everyone my mom knows something.

sometimes, when we get older, we discover that things that seemed normal were toxic manifestations of a unhealthy relationship.

this especially happens when a person is going on a path of self realiziation.

the reason is that you are becoming more confident, and thus are trusting more and more your own judgment, while building up borders. others arent menat to cross.

people that only know your old complacment self cant accept that.

1. listen to people. they tell you who they are.
2. mark how often a person doesnt accept you saying no.
3. trying to change your mind by convincing you of advantages you dont even want is not okay
4. you have to follow up your no by consequences
5. keep attention how many times a person puts you in a bad position
6. take notes with arguments for yourself if you have to. just for your own vizulization

I had notes on my bathroom mirror how an when and in which way my friend took advantage of my naivity.

it was shocking how many times i let that slide because i just wasnt sure if i understood the situation wrong.

same goes for family. i blocked my mom, that why i write this whole thing in the first place.

ok good luck

ps. dont discuss it with your mom. do what you did, tell friends or seek help with other people.

dont make an issue about it. just take note, write the incident down somewhere, and what you think about it. then wait for the next incident, and write that down. see if there is a pattern.

youre autistic for a good reason, embrace that. analyze the situation, be aware that your mom has a perfectly logical reason why she is acting this way. but she sure doesnt want to hear that reason. so thats for you to figure out. if you have it figured out, you can deal with it, because it is a system.

Today, I overheard my mom talking loudly on a video call to my brother and his wife, catching up and sharing their latest news. Apparently her latest news included the fact that I have been diagnosed with ASD.

The way I respond to this is pretty simple; The people around me know I have little need for conversation. I can talk to people and sometimes enjoy it but I can very well not make conversation with people. Disclosing my secrets or misrepresenting my statements is grounds for no further conversation beyond simple practical utility.

In my experience NTs generally assume there's not a privacy restriction unless explicitly stated. Even if not the explicit statement further grounds the decision to make minimal conversation should they violate your trust in that way.

she also mentioned that I've been less conversational lately, which she attributes to my diagnosis and to me no longer wanting to make the effort necessary to talk to neurotypical people

You were recently diagnosed with a second condition that affects your willingness to converse. She already knows you have one and that it's been significantly affecting you lately. Does she know how autism affects interpersonal interaction? Does she think you've developed autism recently? Does she doubt the diagnosis?

I'm also not sure how to move forward with this information in any way without it seeming like I was eavesdropping - which I wasn't intentionally doing,

I have sensitive hearing and I live in an area where most people don't have inside voices. If I'm not wearing my headphones or hyperfocusing on something I can hear people trying to be quiet a floor away. I don't know if you're the same way but I agree with Cagi, if a conversation was meant to be private it should be conducted where it wouldn't be overheard. It'd be eavesdropping only if an attempt to do that was made and you had made intentional actions to subvert that effort. Eavesdropping is an intentional act, overhearing is an autonomic act.

but as it is I don't feel comfortable raising the subject, or noticeably increasing my level of masking (to accomodate her apparent discomfort with me not doing so),

That's entirely up to you how to deal with it. I try to mask less around people I feel safe around. So far I think it's going well. Does she scrutinize things that spontaneously start going her way? If not it may just not come up. If so you could be honest about overhearing her or assert that you were trying to think about how she felt about your recent behavior.

I haven't yet told him, and now I'm worried that he's going to take it as me no longer socializing with neurotypical family members (even though the arrangement was made before my diagnosis).

You could call him to share the diagnosis and 'play dumb' about him already knowing. I don't know how far just to your brother's city is but you could offer an alternative get-together for later and explain that last year's complications have made you want this trip to be simplified.