AITA for telling my ex’s sterile affair partner to have her own daughter if she wants to share cheerleading with one?

My ex (44M) cheated on me (40F) and ended our marriage so he could be with his affair partner/wife Jen (42F). This happened several years ago when our kids were very young. My ex gets our kids 6 days a month. He works out of state frequently so this was the most consistent schedule where our kids would be with a parent (me or ex) instead of being left with a babysitter or his wife.

According to my ex and Jen she is sterile and can never have kids. I never asked but they offered this up in hopes I would “share” the kids with her more and encourage them to embrace Jen as their second mom. I have not done this and I have told them we are not friends and they are not to expect favors from me after going behind my back and doing what they did. Jen was someone I knew before learning the truth. She was dating someone in my ex’s friend circle and made a point to get to know me. I found out why after. She was expecting us being friends would help me not to hate her afterward.

I bring all this up because of what’s currently going on. Jen was a big cheerleader in her youth and volunteers with local cheer groups. She wants my daughter (10) to get involved in cheer. My daughter told me about it the other week because Jen was trying to make her go and my ex was backing Jen on it. She told me she didn’t want to and she needed my help. All the kids are aware of the fact stuff like that has to be agreed on by both me and their dad.

I reached out and told my ex our daughter will not be put into cheer against her will and that he needs to stop pressuring her to join. He didn’t respond back the way he’s supposed to (through app) so I noted his reply on the app and got a lot of cussing back.

Jen tried to call me but I didn’t answer. She approached me a few days later while we were in the same store and she told me I can’t keep punishing her by depriving her of my children. She said she’s been in their lives since they were little and she has every right to bond with them and share stuff with them like that. I told her she does not get to force my kids into stuff like that against their will. I walked away and she followed me around for a bit and told me how it was her dream to share cheer with a daughter and all the crap that I don’t care about. I told her she should have a daughter of her own if she wants to share it and leave mine alone.

She stopped following me after that and I heard from ex a few times after saying I was cruel to say that to her when I know she can’t have children.

AITA?