"AITA for not wanting my ex's mistress at my daughter's birthday party?"

My ex husband (32m) and I (33f) were together 13 years, married for 7.5. We had two beautiful daughters who are now 6 and almost 4. Earlier this year, I was fighting to save the marriage and he was being standoffish, cold, borderline emotionally abusive and refusing to communicate or work with me. One day I decided I had had enough, I asked him to leave and he was happy to go.

We have always been on the same page as far as coparenting amicably, not using the children as weapons, fair visitation, etc. He's a great father, but a terrible partner. In May, I find out he's dating someone-- seems a little fast to me but not a big deal. She's someone he knew from work, he promised nothing was happening when we were still married and I believed him.

A month later, he informs me she's pregnant! Doing some rough math by the due date, they conceived 6 weeks after he moved out. Again, not great decision making on his part, it's a lot for the kids to process when they don't even fully understand why their parents dont live together anymore.

In July, the bomb drops. I find out that not only was he sleeping with this girl 6 months before he and I even split up, he had previously gotten her pregnant and taken her for an abortion a few months before I asked him to move out. This was tough to deal with. I don't think a person ever really recovers from that devastating blow to their self esteem.

I have always encouraged my kids to have a relationship with this woman, her existing children, and the new baby. However, I dont care to have a relationship with her at this point. I might get there but I'm just not there yet. I have been struggling with my mental health lately and I'm trying my best to just deal with the day to day sometimes.

I have primary physical custody of the kids, I have 2 jobs, 3 dogs and I take care of our previously shared house on my own. I have a lot on my plate. Ex husband moved in with his parents after the split-- almost 15 months on he's still living there. His parents have a pool. 6 year old wants a pool party/slumber party for her birthday this week.

We planned the party so that the kids can go swimming at his (parents) place, then walk the 2 blocks to my house and have the slumber party at my place. I planned it this way in the interest of peaceful coparenting, so that my 6yo knows that even though her parents are split, we will always be family.

Ex informs me this week that he wants mistress to be at the party. I said no, I'm not mentally ready for that yet. To be clear-- I don't have a problem with him having a girlfriend (I've been dating someone for 10 months) -- I just haven't developed the strategies to deal with my anger that I feel toward this particular woman. He told me that she's "family now" and I "need to learn how to deal with it."

He also stated it's his call because it's "his" house. AITA for putting my foot down and saying I'm just not ready for this yet? I don't want my kids to see me upset on what's supposed to be a happy day.

What do you think? AITA? This is what top commenters had to say:

U-r-a-scrub said:

NAH. In your eyes she is still the "mistress" that ruined your marriage. I can see you feel some type of way about that. The thing is, now that mistress has evolved into a WIFE. Whether you like it or not she's there to stay. You can choose to suck it up and participate in your family's life, or you can chose not to. No one would blame you. This party is at his house so you can't control who gets to be there.

OP responded:

She hasn't evolved into a wife. Technically I'm still the wife... they don't even live together!! Despite my best effort to not be the wife anymore he doesn't seem to be able to get his paperwork together for his part of that!

bratlygirl said:

I think separate parties in the future will be a good idea. I’ve been through all of this as well. Sorry, it gets easier.

1meower said:

NTA - This is a horrible situation and I’m so sorry that you’re having to deal with all of this. You’re definitely not the asshole but I think you need to suck it up and just be grateful that he’s her problem now. The other option would be to not go. Let them have they’re pool party and have cake at your house for the slumber party portion. Either way, the day won’t be easy and I hope find the strength to endure it.

OP responded:

Thank you. I think part of my issue is that we have known about this party for weeks, he chose today 3 hours beforehand to drop this on me. I know I'll get to a point where I can be kind to her, I'm not an inherently shitty person. I just don't think I want the first experience to be at my kid's party, where I can't escape or take a breather, and where I'm responsible for a bunch of other peoples kids all night.

[deleted] said:

NTA but did she know he was married and had kids? because if she didn't you have no reason to be mad at her.

OP responded:

She definitely did, they worked together and we saw her socially

Edit from OP:

When he asked me earlier in the week if he could invite her, I offered to just change the party venue to my house and he told me not to. Now 2 hours before the party he is telling me she is coming.

And here are some updates she posted in the comments:

Party is in an hour. I tried to change the venue when he told me he was inviting her. He said no, it's fine, I wont invite her but it's the last thing I wont invite her to. I was fine with that. Day of and he's trying to change his mind. Unfortunately not a lot.of options at this point :(

My whole family is going to be there and I just don't want there to be an awkward hostile environment. I know I'll get to a place where I can be around her... just not today!

After the party:

She ended up not coming! It went very well and my ex and I got along fine. I'm glad I posted though, got some good advice and support!!

Phew!