I'm 40F, with a 4 year old son. My sister is 42F, with four children aged between 2 and 7 years old. We live a little over an hour apart from each other. We used to be close, but our relationship hasn't been great in the last few years, because we dislike each other's partners. Nonetheless, we have always made a point of making sure that this didn't get in the way of family events for our children.

I have always attended all of my niblings' birthday parties, and have only missed a couple on occasions when I was sick, or once when my car broke down. On average, I go down to events at my sister's home at least 4-6 times a year for events they host. She has only visited my house twice since my son was born - once right after I gave birth, and then for his birthday party last year when he turned 3. This is not for a lack of invitations. It has been a source of tension between us that she does not reciprocate visits, but I have tried to be understanding given that she is very busy with four kids.

My son turned 4 last month, and we arranged a birthday party for him, inviting a few friends but mostly family. My sister RSVPd for the party saying that she would bring two of her children. The other two would go with their father to another child's birthday party they had already RSVPd to. This other party was for a child of one of my sister's colleagues/friends, and I understand he is quite close with one of her sons. I was a bit hurt that she would prioritise that party over my son's, but I accepted she was at least meeting me halfway, and did not give her any grief about it.

The day before my son's party, my sister fell ill. As a result, she was not well enough to come. However, the practical upshot was that she and her husband chose for him to take all four of the children to the other child's birthday party. None of them attended their cousin's 4th birthday. We had only planned a smallish event, so this meant that there were only about 4 child guests. (They still had a good time.)

My sister did not apologise for her choice to send all four of her children to a different party. She does not accept that this was in any way wrong. Her attitude was, oh well, couldn't be helped. When I put to her that what she'd done was extremely hurtful and was, in fact, a choice she had made to prioritise her friend's child over her sister's child, she just turned it around on me and raised the time that I had missed her son's birthday when my car broke down. She refused to acknowledge that this isn't the same, and that wasn't a choice I made. (She also tried to blame her kids for preferring to go to the other party, but I told her that she's the parent, and the choice didn't lie with kids aged 4 and 6 years old). I certainly never chose to miss one of her kid's events so that I could go to an event for some other child.

The week after this, it was my niece's birthday party. My partner and I had originally planned to go, but we decided not to, because we were feeling very hurt about what happened, and the ongoing total lack of any reciprocity or care from my sister's family. I did send a gift for my niece.

Sister got mad at me, accused me of acting out of spite/malice/revenge by "boycotting" her daughter's party. I said - what did you expect me to do after what you did last week? She said fine, let's just go back to not talking. So, we're not talking.

AITA?