This is going to be a little long, but please help me. I’m usually great at things like this but my rage has me scattered.

My first husband left me when I was 20 weeks pregnant with our only child together. We divorced when she was 3 months old and he has gone on to treat her as less than, pretty much her whole life. Things became more pronounced when he married his second wife and they had kids together. Examples: getting family photos done, without her. Having three gender reveals for their babies, never invited her. Vacations to Florida without her. Per custody agreement, she’s there from Sunday evening til Tuesday after school, they got rid of her bed at his haus. I could go on for about an hour. The only light in this situation is my forever husband came into her life when she was 4yo, he’s grown into being an actual loving, supportive father to her.

When I announced my next two pregnancies, new wife followed up 3-4 weeks later with the same news. As a result, my next two kids are the same age as the ex’s. And wouldn’t you know but, my kids and his kids LOVE each other. Ex’s kids come over a lot and whereas it is very very strange for me to see little versions of him running around, it’s fine. I don’t mind a bit, I’m glad eldest’s siblings get along and nothing wrong with more friends.

Here’s the problem. Eldest turns 18 this month, on a Sunday. Her second to youngest sibling over there turns 9 this month as well, and I was not surprised when my 9yo got invited to the cross-sibling’s party. Would have every intention of allowing mine to attend. BUT! Ex is throwing 9yo party on eldest’s birthday exact birth date. The other child birthday is on a different weekend’s Friday this month. (I mention to emphasize that there is not such a close overlap that it would make sense to have it on eldest’s birthday weekend let alone the actual date).

I am so angry and devastated for her. He’s hurt her so much, and there’s very little doubt that this was not deliberate to target her. He’s actually told her how excited he is to not have to pay $400/month in child support anymore.

I need help with the perfect poison pill RSVP. Nothing to reference the children at all, this is obvs none of their faults. I want to go nuclear on my ex-husband her stepmother with words. I want to hurt them and point out what huge assholes they are. Thanks Reddit.