To have nothing further to do with them?

Friends that you choose and who choose you through shared values, sense of humour, commonality re hobbies, lifestyles, political views, love of cake, fear of clowns, anything.

Blood links mean nothing compared to things that really matter when the chips are down.

If I were in crisis, and DP wasn't available, I'd call my best friend. She'd then deal with my family if necessary, but she'd be my first call. We chose each other.

DO you accept many children have parties just for school friends?
My children have about 35 cousins so there was never any way that parties would have been for family members too. Mine just had school friends.
I do understand you’re vulnerable given you clearly feel lonely from being an only child. I think looking at forging local relationships would be really beneficial.
I will add, I’m also autistic. But part of being ND is learning how other people think, just as other people should educate themselves on how we often react. I think you are being over sensitive and I think you overreacted. I think you set your dd a poor example by going upstairs.
I don’t suppose you’ll respond to this as you’ve not responded to my other comments but you do seem very blinkered and unwilling to accept other views.

I think she wouldn't like the answer, and out of politeness they'd never give it.

@Pouticel why don't you just ask if there is a problem that you're unaware of/missing?

If you truly feel ready to walk away then surely you have nothing to lose? There might be something else going on that you're overlooking altogether

I have a lot of cousins, we saw a fair bit of each other when we were younger, used to stay at their houses for a time during the summers etc….not close to anyone of them now (no fallout) and never see them

@Pouticel there are going to be so many disappointments of various magnitudes for your DD as she grows up. You have to be able to be someone she can share it with, without it becoming about you.

DD3 has been terribly damaged by an experience at school. It completely derailed her education. She was a grade 8/9 student and now has had time completely out of school, has had to move schools, is a year behind and is not going to get more than a couple of GCSEs. I could easily wallow with her in the unfairness of it all, and I did allow her to have all her feelings. But we're almost 2 years on now, so I'm gently challenging the feelings that she was targeted and deliberately hurt because I genuinely don't think it was the case. She was in the wrong place at the wrong time and any child in that place at that time would have been treated the same. So we talk it through and I gently remind her that she wasn't hated, she was just seen as a threat.

You have the opportunity to change how your DD views this situation. It won't do her any good to think that her cousin was wrong for not inviting her, because she wasn't. She should not feel guilty for having a birthday party that didn't include her cousin, followed by a family gathering. You are projecting your feeling of rejection on to this situation. You can choose to stop that.

She shouldn’t expect a relationship with them just because they are family but they should expect her to raise their child in the event of an emergency because they are family.

Do you see the contradiction?

OP, I get that you might not understand social conventions if you are autistic, but there are so many people in this thread explaining over and over again that it's very common to have a party for school friends, and then a separate tea with family, and not invite family to the party with school friends.

You have not acknowledged anyone who has said this even though it's what most people are saying. Most people think you are being unreasonable and not understanding that their behaviour is completely normal.

Instead, you are continuing to play the victim and say that trying to explain the situation to your child would be lying.

I despair.

Exactly! But the OP seems to have a fixed definition with the requisite obligations attached that she hasn't explained.

I honestly think you expect too much, some people lead very busy lives, lower your expectations and accept that they will just see each other 3-4 times a year and still be friends, it might be even better like that as then they might look forward to these visits more

I don't know because I think there are levels of love, it's not an all encompassing one size fits all thing. I definitely love some members of my family more than others. Some I feel nothing for and some I was totally taken aback by how much I loved them after they were gone. Same goes for friends I love some more than others but I feel some degree of something for all of them.

It's complicated and impossible to articulate, as I suspect I've just proved!

@Pouticel
You've had loads of responses saying a 'class only ' party is completely normal.

This was a teachable moment for your DC that she won't always be invited to the party ...... And that's fine.

All the other stuff is you projecting massively and where you really need to reframe your thoughts. You cannot control your SIL.

They’re supposed to love us - or at least love their niece - and they clearly don’t.
No, there is no rule book that says they are supposed to love you, or your DC.

Why will you not accept that it was a school friends party?

It was probably kept secret because of the chance of an extreme over reaction if it had been talked about in a normal way. Which is exactly what happened.
Your DC can't just have one friend, and that one her cousin. And never a birthday party with friends from school. She must feel that already.

ND or not, if you want her to have a normal, friendly childhood, you and your DH need to put yourselves second, and start planning for the next birthday. And Brownies and play dates and all the rest. You just have to. And, if it makes you feel any better, half the other parents you meet will stress and worry about parties and playdates and how they'll ever pull it off, or afford it, but the difference is that they will grit their teeth and get on with it, because it helps their kids.

I’ve had this situation before. But my in laws went on a family trip to with all grandparents etc and then a cousin let it slip it was a secret. My child was so upset. I was infuriated at how anyone would want to exclude a child especially their family. I done the same. Told them I was angry and blocked them etc. we didn’t talk for a year.

However in hindsight what I should have done was ask them if there was an issue that they'd like to discuss because the relationship meant alot to us. I also wouldn’t cut things off for the children’s sake. It’s not their fault, so I’d leave an opening there for if and whenever they did want to engage. But maybe not mention them as much around my child so they didn’t expect to see them as much.

If you were so worried about your kid not having anyone after you have gone, why didn't you have two kids? You seem to be obsessed with your DC having someone to play with.

I don't agree. I like my nieces even when they are being the typical bratty kids of their age. I find them quite fun and interesting on occasion, but love? I don't know. You'd need to define what you mean by love for me to answer that.

I do like the effect that having them has had on my sister though, she's way more amusing now than she was.

I know that you won't believe this but they probably do love her to some degree. They just don't express it in ways that you would like them to.

Because your child will be more hurt by your reaction than they were by finding out that there was a party. You could have said anything. "Oh, it was far too far to go on a week night, DD", or "We're having a special party now", or "The party was school friends only this time".

Your upset shouldn't be your DD's problem and your SIL didn't owe your DD an invitation.

I have read all your updates OP and I definitely see that you are feeling really hurt. My daughter and I are autistic and I do empathise with some of what you’re saying but I think you have overlooked a couple issues. First is that you are extremely black and white. Cousins can have many different relationships and don’t need to see each other regularly to feel close. The other is that - as far as you’ve said anyway - you have no idea what this cousin actually wanted for her party. It would be a very different issue if she asked to include your daughter and her parents refused.

(also you and your husband should just sell your car and get a bigger one. I have a zafira and it’s brilliant for this sort of thing)

My kids don’t have any first cousins and have no memories of their second cousins. We immigrated before they were born and haven’t really seen our extended family since. I do think about how eventually they’ll only have that connection with each other and get a bit worried about it… but then I remember that there’s literally millions of potential futures and how do I know which thing is the most worrying. I personally think you can save the energy you’re spending on worrying about this and focus on how to create found family for you and your daughter. Does she have any clubs she enjoys? Could you join a parent child tennis club or little picking volunteer groups or find a craft class to try? Or any other of the many, many options. You cannot create the relationship you’re imagining - personally I think it’s needlessly dramatic to storm off but it doesn’t really matter - they aren’t what you need and you should try to find that elsewhere.

I have an autistic family member and I love them with all my heart. If OP hadn't mentioned they were autistic I'd have guessed because a lot of their phrasing and fixation are very similar to my loved one.

But I'd still say every word I've said here to them irl, including the fact that they must be giving themselves a headache.